Incorrect match for punctuation.definition.string.begin.latex

[gpoore]

In LaTeX.tmLanguage.json, the token punctuation.definition.string.begin.latex currently has the begin pattern (?<!\\\\)(\\`\\`). I suggest extending the negative lookbehind to eliminate incorrect matches. I just encountered \catcode`` , and \string`` would be similar. A begin pattern like (?<!\\\\|\\\\catcode|\\\\string)(\\`\\`) would be better. There may be other situations that could cause an incorrect match, but I expect that this modification would cover most common cases.