Be explicit about 'in-place'

On darwin, sed expects an argument for '-i'. Make it empty.

Change-Id: I5dc6cdf667a754b2624f1767eb6e8025df48e308

tools/ftfy.sh

@@ -34,7 +34,7 @@ vpx_style() {
          --align-pointer=name \
          --indent-preprocessor --convert-tabs --indent-labels \
          --suffix=none --quiet "$@"
-  sed -i 's/[[:space:]]\{1,\},/,/g' "$@"
+  sed -i "" 's/[[:space:]]\{1,\},/,/g' "$@"
 }