Added support for s regex flag (#1846)

This adds support for the ES2018 `s` (dotall) flag for regular expressions.

components/prism-javascript.js

@@ -26,7 +26,7 @@ Prism.languages.javascript['class-name'][0].pattern = /(\b(?:class|interface|ext
 
 Prism.languages.insertBefore('javascript', 'keyword', {
 	'regex': {
-		pattern: /((?:^|[^$\w\xA0-\uFFFF."'\])\s])\s*)\/(\[(?:[^\]\\\r\n]|\\.)*]|\\.|[^/\\\[\r\n])+\/[gimyu]{0,5}(?=\s*($|[\r\n,.;})\]]))/,
+		pattern: /((?:^|[^$\w\xA0-\uFFFF."'\])\s])\s*)\/(\[(?:[^\]\\\r\n]|\\.)*]|\\.|[^/\\\[\r\n])+\/[gimyus]{0,6}(?=\s*($|[\r\n,.;})\]]))/,
 		lookbehind: true,
 		greedy: true
 	},

prism.js

@@ -787,7 +787,7 @@ Prism.languages.javascript['class-name'][0].pattern = /(\b(?:class|interface|ext
 
 Prism.languages.insertBefore('javascript', 'keyword', {
 	'regex': {
-		pattern: /((?:^|[^$\w\xA0-\uFFFF."'\])\s])\s*)\/(\[(?:[^\]\\\r\n]|\\.)*]|\\.|[^/\\\[\r\n])+\/[gimyu]{0,5}(?=\s*($|[\r\n,.;})\]]))/,
+		pattern: /((?:^|[^$\w\xA0-\uFFFF."'\])\s])\s*)\/(\[(?:[^\]\\\r\n]|\\.)*]|\\.|[^/\\\[\r\n])+\/[gimyus]{0,6}(?=\s*($|[\r\n,.;})\]]))/,
 		lookbehind: true,
 		greedy: true
 	},

tests/languages/javascript/regex_feature.test

@@ -1,5 +1,5 @@
 /foo bar/;
-/foo/gimyu,
+/foo/gimyus,
 /[\[\]]{2,4}(?:foo)*/;
 /foo"test"bar/;
 /foo\//;
@@ -13,7 +13,7 @@
 
 [
 	["regex", "/foo bar/"], ["punctuation", ";"],
-	["regex", "/foo/gimyu"], ["punctuation", ","],
+	["regex", "/foo/gimyus"], ["punctuation", ","],
 	["regex", "/[\\[\\]]{2,4}(?:foo)*/"], ["punctuation", ";"],
 	["regex", "/foo\"test\"bar/"], ["punctuation", ";"],
 	["regex", "/foo\\//"], ["punctuation", ";"],