update docs

.travis.yml

@@ -8,7 +8,3 @@ node_js:
   - '10'
   - '9'
   - '8'
-  - '7'
-  - '6'
-  - '5'
-  - '4'

.verb.md

@@ -46,13 +46,14 @@ If you're interested in learning more about [character classes](http://www.regul
 
 ### Heavily tested
 
-As of {%= date() %}, this library runs [2,783,483 test assertions](./test/test.js) against generated regex-ranges to provide brute-force verification that results are indeed correct. 
+As of {%= date() %}, this library runs [>1m test assertions](./test/test.js) against generated regex-ranges to provide brute-force verification that results are correct. 
 
-Tests run in ~580ms on my MacBook Pro, 2.5 GHz Intel Core i7.
+Tests run in ~280ms on my MacBook Pro, 2.5 GHz Intel Core i7.
 
-### Highly optimized
+### Optimized
+
+Generated regular expressions are optimized:
 
-Generated regular expressions are highly optimized:
 - duplicate sequences and character classes are reduced using quantifiers
 - smart enough to use `?` conditionals when number(s) or range(s) can be positive or negative
 - uses fragment caching to avoid processing the same exact string more than once 
@@ -75,11 +76,11 @@ The main export is a function that takes two integers: the `min` value and `max`
 const source = toRegexRange('15', '95');
 //=> 1[5-9]|[2-8][0-9]|9[0-5]
 
-const re = new RegExp('^' + source + '$');
-console.log(re.test('14')); //=> false
-console.log(re.test('50')); //=> true
-console.log(re.test('94')); //=> true
-console.log(re.test('96')); //=> false
+const regex = new RegExp(`^${source}$`);
+console.log(regex.test('14')); //=> false
+console.log(regex.test('50')); //=> true
+console.log(regex.test('94')); //=> true
+console.log(regex.test('96')); //=> false
 ```
 
 ## Options
@@ -122,35 +123,32 @@ console.log(toRegexRange('0', '999999', { shorthand: true }));
 
 **Default**: `true`
 
-This option only applies to **negative zero-padded ranges**. By default, when a negative zero-padded range is defined, the number of leading zeros is relaxed using `-0*`.  
+This option relaxes matching for leading zeros when when ranges are zero-padded.  
 
 ```js
-console.log(toRegexRange('-001', '100'));
-//=> -0*1|0{2}[0-9]|0[1-9][0-9]|100
-
-console.log(toRegexRange('-001', '100', {relaxZeros: false}));
-//=> -0{2}1|0{2}[0-9]|0[1-9][0-9]|100
+const source = toRegexRange('-0010', '0010');
+const regex = new RegExp(`^${source}$`);
+console.log(regex.test('-10')); //=> true
+console.log(regex.test('-010')); //=> true
+console.log(regex.test('-0010')); //=> true
+console.log(regex.test('10')); //=> true
+console.log(regex.test('010')); //=> true
+console.log(regex.test('0010')); //=> true
 ```
 
-<details>
-  <summary><strong>Why are zeros relaxed for negative zero-padded ranges by default?</strong></summary>
-
-Consider the following.
+When `relaxZeros` is false, matching is strict:
 
 ```js
-const regex = toRegexRange('-001', '100');
+const source = toRegexRange('-0010', '0010', { relaxZeros: false });
+const regex = new RegExp(`^${source}$`);
+console.log(regex.test('-10')); //=> false
+console.log(regex.test('-010')); //=> false
+console.log(regex.test('-0010')); //=> true
+console.log(regex.test('10')); //=> false
+console.log(regex.test('010')); //=> false
+console.log(regex.test('0010')); //=> true
 ```
 
-_Note that `-001` and `100` are both three digits long_. 
-
-In most zero-padding implementations, only a single leading zero is enough to indicate that zero-padding should be applied. Thus, the leading zeros would be "corrected" on the negative range in the example to `-01`, instead of `-001`, to make total length of each string no greater than the length of the largest number in the range (in other words, `-001` is 4 digits, but `100` is only three digits). 
-
-If zeros were not relaxed by default, you might expect the resulting regex of the above pattern to match `-001` - given that it's defined that way in the arguments - _but it wouldn't_. It would, however, match `-01`. This gets even more ambiguous with large ranges, like `-01` to `1000000`.
-
-Thus, we relax zeros by default to provide a more predictable experience for users. 
-
-</details>
-
 ## Examples
 
 {%= examples() %}
@@ -179,6 +177,10 @@ This library does not support steps (increments). A pr to add support would be w
 
 ## History
 
+### v5.0.0 - 2019-04-07
+
+Optimizations. Updated code to use newer ES features. 
+
 ### v2.0.0 - 2017-04-21
 
 **New features**