Update JsShrink external library.

Summary: It seems that there was a [[17cbfacae6 | recent-ish commit]] to the `JsShrink` external library. I'm not sure what this commit actually achieves, but we may as well bring it upstream.

Test Plan: Eyeball it.

Reviewers: vrana, epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9414

externals/JsShrink/jsShrink.php

@@ -13,7 +13,11 @@ function jsShrink($input) {
 		(?:
 			(^|[-+\([{}=,:;!%^&*|?~]|/(?![/*])|return|throw) # context before regexp
 			(?:\s|//[^\n]*+\n|/\*(?:[^*]|\*(?!/))*+\*/)* # optional space
-			(/(?![/*])(?:\\\\[^\n]|[^[\n/\\\\]|\[(?:\\\\[^\n]|[^]])++)+/) # regexp
+			(/(?![/*])(?:
+				\\\\[^\n]
+				|[^[\n/\\\\]++
+				|\[(?:\\\\[^\n]|[^]])++
+			)+/) # regexp
 			|(^
 				|\'(?:\\\\.|[^\n\'\\\\])*\'
 				|"(?:\\\\.|[^\n"\\\\])*"