Support comma in go template (e.g. for range)

```
{{ range $idx, $value := $variable }}
Hello {{ $idx }}
{{ end }}
```

Author: cmaster11

Diff for: lexers/g/go.go

@@ -80,7 +80,7 @@ var goTemplateRules = Rules{
 		{`\s+`, Whitespace, nil},
 		{`\(`, Operator, Push("subexpression")},
 		{`(range|if|else|while|with|template|end|true|false|nil|and|call|html|index|js|len|not|or|print|printf|println|urlquery|eq|ne|lt|le|gt|ge)\b`, Keyword, nil},
-		{`\||:?=`, Operator, nil},
+		{`\||:?=|,`, Operator, nil},
 		{`[$]?[^\W\d]\w*`, NameOther, nil},
 		{`[$]?\.(?:[^\W\d]\w*)?`, NameAttribute, nil},
 		{`"(\\\\|\\"|[^"])*"`, LiteralString, nil},

Diff for: lexers/testdata/go-text-template.actual

@@ -3,4 +3,8 @@
 */}}
 
 {{ $myVar := 2 }}
-{{ $myVar = 4 }}
+{{ $myVar = 4 }}
+
+{{ range $idx, $value := $variable }}
+Hello {{ $idx }}
+{{ end }}

Diff for: lexers/testdata/go-text-template.expected

@@ -19,5 +19,32 @@
   {"type":"TextWhitespace","value":" "},
   {"type":"NameOther","value":"4"},
   {"type":"TextWhitespace","value":" "},
+  {"type":"CommentPreproc","value":"}}"},
+  {"type":"Other","value":"\n\n"},
+  {"type":"CommentPreproc","value":"{{"},
+  {"type":"TextWhitespace","value":" "},
+  {"type":"Keyword","value":"range"},
+  {"type":"TextWhitespace","value":" "},
+  {"type":"NameOther","value":"$idx"},
+  {"type":"Operator","value":","},
+  {"type":"TextWhitespace","value":" "},
+  {"type":"NameOther","value":"$value"},
+  {"type":"TextWhitespace","value":" "},
+  {"type":"Operator","value":":="},
+  {"type":"TextWhitespace","value":" "},
+  {"type":"NameOther","value":"$variable"},
+  {"type":"TextWhitespace","value":" "},
+  {"type":"CommentPreproc","value":"}}"},
+  {"type":"Other","value":"\nHello "},
+  {"type":"CommentPreproc","value":"{{"},
+  {"type":"TextWhitespace","value":" "},
+  {"type":"NameOther","value":"$idx"},
+  {"type":"TextWhitespace","value":" "},
+  {"type":"CommentPreproc","value":"}}"},
+  {"type":"Other","value":"\n"},
+  {"type":"CommentPreproc","value":"{{"},
+  {"type":"TextWhitespace","value":" "},
+  {"type":"Keyword","value":"end"},
+  {"type":"TextWhitespace","value":" "},
   {"type":"CommentPreproc","value":"}}"}
 ]