Fetch fixture grammars on appveyor

script/fetch-fixtures.cmd

@@ -0,0 +1,26 @@
+@echo off
+
+call:fetch_grammar javascript master
+call:fetch_grammar json       master
+call:fetch_grammar c          master
+call:fetch_grammar cpp        master
+call:fetch_grammar python     master
+call:fetch_grammar go         master
+call:fetch_grammar ruby       master
+call:fetch_grammar typescript master
+call:fetch_grammar bash       master
+EXIT /B 0
+
+:fetch_grammar
+SETLOCAL
+SET grammar_dir=test\fixtures\grammars\%~1
+SET grammar_url=https://github.com/tree-sitter/tree-sitter-%~1
+SET grammar_branch=%~2
+@IF NOT EXIST %grammar_dir% (
+  git clone %grammar_url% %grammar_dir% --depth=1
+)
+pushd %grammar_dir%
+git fetch origin %2 --depth=1
+git reset --hard origin/%grammar_branch%
+popd
+EXIT /B 0