fix: Support GNU diff 3.11+

Starting from diff 3.11 filenames for `diff -r --brief` are wrapped with
apostrophes, so regex to take filenames doesn't match.

Author: andrey-starodubtsev

plugin/dirdiff.vim

@@ -784,6 +784,11 @@ function! <SID>GetFileNameFromLine(AB, line)
     elseif <SID>IsDiffer(a:line)
         let regex = '^.*' . s:DirDiffDifferLine . '\[A\]\(.*\)' . s:DirDiffDifferAndLine . '\[B\]\(.*\)' . s:DirDiffDifferEndLine . '.*$'
         let fileToProcess = substitute(a:line, regex, '\1', '')
+        if fileToProcess == a:line
+            " Didn't match, try filename in apostrophes
+            let regex = '^.*' . s:DirDiffDifferLine . "'\\[A\\]\\(.*\\)'" . s:DirDiffDifferAndLine . "'\\[B\\]\\(.*\\)'" . s:DirDiffDifferEndLine . '.*$'
+            let fileToProcess = substitute(a:line, regex, '\1', '')
+        endif
     else
     endif