Checker luac: fix errorformat.

Newer versions of luac prepend error messages with the actual name of
the executable.

Reference: http://www.lua.org/source/5.3/luac.c.html#fatal

plugin/syntastic.vim

@@ -19,7 +19,7 @@ if has('reltime')
     lockvar! g:_SYNTASTIC_START
 endif
 
-let g:_SYNTASTIC_VERSION = '3.7.0-224'
+let g:_SYNTASTIC_VERSION = '3.7.0-225'
 lockvar g:_SYNTASTIC_VERSION
 
 " Sanity checks {{{1

syntax_checkers/lua/luac.vim

@@ -47,7 +47,7 @@ endfunction
 function! SyntaxCheckers_lua_luac_GetLocList() dict
     let makeprg = self.makeprgBuild({ 'args_after': '-p' })
 
-    let errorformat = 'luac: %#%f:%l: %m'
+    let errorformat = '%*\f: %#%f:%l: %m'
 
     return SyntasticMake({
         \ 'makeprg': makeprg,