Don’t use --invert-grep.

It is not supported on git 1.8.3.1

Author: mcepl

git-fixup

@@ -34,7 +34,8 @@ function fixup_candidates_lines () {
 function fixup_candidates_files () {
     git diff --cached --name-only | (
         while read file; do
-            git rev-list -n 1 -E --invert-grep --grep='^(fixup|squash)' $rev_range -- $file
+            git rev-list $rev_range -- $file \
+                | grep -v -f <(git rev-list -E --grep='^(fixup|squash)' $rev_range -- $file )
         done
     ) | sed 's/^/F /g'
 }