Fix .arclint on Windows

Run "bash myscript.sh". This will work if bash is on PATH, which it
probably is, since developers have to use git.

Reviewed By: scott.linder

Differential Revision: https://reviews.llvm.org/D78846

.arclint

@@ -2,7 +2,7 @@
   "linters": {
     "clang-format": {
       "type": "script-and-regex",
-      "script-and-regex.script": "utils/arcanist/clang-format.sh",
+      "script-and-regex.script": "bash utils/arcanist/clang-format.sh",
       "script-and-regex.regex": "/^(?P<severity>[[:alpha:]]+)\n(?P<message>[^\n]+)\n(====|(?P<line>\\d),(?P<char>\\d)\n(?P<original>.*)>>>>\n(?P<replacement>.*)<<<<\n)$/s",
       "include": [
         "(\\.(cc|cpp|h)$)"