Fix highlighting for '=>' and some operators

Refs #558

Author: maxbrunsfeld

grammars/tree-sitter-javascript.cson

@@ -99,12 +99,14 @@ scopes:
   '"class"': 'storage.type'
   '"const"': 'storage.modifier'
   '"static"': 'storage.modifier'
-  '"function"': 'storage.type'
-
-  '"+"': 'keyword.operator'
-  '"-"': 'keyword.operator'
-  '"*"': 'keyword.operator'
-  '"/"': 'keyword.operator'
+  '"function"': 'storage.type.function'
+  '"=>"': 'storage.type.function'
+
+  '"="': 'keyword.operator.js'
+  '"+"': 'keyword.operator.js'
+  '"-"': 'keyword.operator.js'
+  '"*"': 'keyword.operator.js'
+  '"/"': 'keyword.operator.js'
   '"in"': 'keyword.operator.in'
   '"instanceof"': 'keyword.operator.instanceof'
   '"of"': 'keyword.operator.of'