feat(watchForUpdates): add watchForUpdatesNonPersistent option

  * add option that makes fs watch non persistent (avoid stuck process)
  * fix UT
  * fix a deprecation message from sinon sandbox
  * update doc
  * update package-lock file for travis build in node 10

(nonPersistentWatcher)

README.md

@@ -74,6 +74,16 @@ var lookup = maxmind.openSync('/path/to/GeoLite2.mmdb', { watchForUpdates: true
 lookup.get('1.1.1.1');
 ```
 
+You also can specify wether the watcher should be persistent or not. If it is persistent, a node process will be blocked in watching state if the watcher is the only thing still running in the program. You can use `watchForUpdatesNonPersistent` option (default `false`) to prevent this behavior.
+```javascript
+var lookup = maxmind.openSync('/path/to/GeoLite2.mmdb', {
+  watchForUpdates: true,
+  watchForUpdateNonPersistent: true,
+});
+lookup.get('1.1.1.1');
+```
+
+
 Also, you can specify custom hook function on database update.
 
 ```javascript

index.js

@@ -31,7 +31,8 @@ exports.open = function(filepath, opts, cb) {
       if (opts.watchForUpdatesHook && typeof opts.watchForUpdatesHook != 'function') {
         throw new Error('opts.watchForUpdatesHook should be a function');
       }
-      fs.watch(filepath, function() {
+      var watcherOptions = {persistent: opts.watchForUpdatesNonPersistent !== true};
+      fs.watch(filepath, watcherOptions, function() {
         fs.readFile(filepath, function(err, database) {
           if (err) return cb(err);
           reader.load(database, opts);
@@ -51,7 +52,8 @@ exports.openSync = function(filepath, opts) {
     if (opts.watchForUpdatesHook && typeof opts.watchForUpdatesHook != 'function') {
       throw new Error('opts.watchForUpdatesHook should be a function');
     }
-    fs.watch(filepath, function() {
+    var watcherOptions = {persistent: opts.watchForUpdatesNonPersistent !== true};
+    fs.watch(filepath, watcherOptions, function() {
       reader.load(fs.readFileSync(filepath), opts);
       if (opts.watchForUpdatesHook) {
         opts.watchForUpdatesHook();