make scheme regex stricter

It now must match `[a-zA-Z0-9+\-.]` as described in the RFC.

This means relative urls that happen to contain ‘:’ are more likely to
be recognised as relative providing they contain a character that does
not satisfy the above

src/url-toolkit.js

@@ -4,7 +4,7 @@
 (function(root) { 
 /* jshint ignore:end */
 
-  var URL_REGEX = /^((?:[^\/;?#]+:)?)(\/\/[^\/\;?#]*)?(.*?)??(;.*?)?(\?.*?)?(#.*?)?$/;
+  var URL_REGEX = /^((?:[a-zA-Z0-9+\-.]+:)?)(\/\/[^\/\;?#]*)?(.*?)??(;.*?)?(\?.*?)?(#.*?)?$/;
   var FIRST_SEGMENT_REGEX = /^([^\/;?#]*)(.*)$/;
   var SLASH_DOT_REGEX = /(?:\/|^)\.(?=\/)/g;
   var SLASH_DOT_DOT_REGEX = /(?:\/|^)\.\.\/(?!\.\.\/).*?(?=\/)/g;

test/url-toolkit.js

@@ -136,6 +136,10 @@ describe('url toolkit', function() {
     test('http://a/b/c/d;p?q', '..', 'http://a/b/');
 
     test('http://a.com/b/cd/e.m3u8?test=1#something', '', 'http://a.com/b/cd/e.m3u8?test=1#something');
+
+    test('http://a.com/b/cd/e.m3u8?test=1#something', 'a_:b', 'http://a.com/b/cd/a_:b');
+    test('http://a.com/b/cd/e.m3u8?test=1#something', 'a:b', 'a:b');
+    test('http://a.com/b/cd/e.m3u8?test=1#something', './a:b', 'http://a.com/b/cd/a:b');
   });
 });