Fix issue where diff preview was broken on mac (#365)

Closes #362

bin/git-forgit

@@ -137,10 +137,10 @@ _forgit_diff() {
     #   oldfile\0
     # We have to do a two-step sed -> tr pipe because OSX's sed implementation does
     # not support the null-character directly.
-    get_files="echo {} | sed 's/\\\\s*\\\\[.]\\\\s*//' | sed 's/  ->  /\\\n/' | tr '\\\n' '\\\0'"
+    get_files="echo {} | sed -e 's/^[[:space:]]*\\\\[[A-Z0-9]*\\\\][[:space:]]*//' | sed 's/  ->  /\\\n/' | tr '\\\n' '\\\0'"
     # Similar to the line above, but only gets a single file from a single line
     # Gets the new name of renamed files
-    get_file="echo {} | sed 's/\\\\s*\\\\[.]\\\\s*//' | sed 's/.*->  //'"
+    get_file="echo {} | sed -e 's/^[[:space:]]*\\\\[[A-Z0-9]*\\\\][[:space:]]*//' | sed 's/.*->  //'"
     # Git stashes are named "stash@{x}", which contains the fzf placeholder "{x}".
     # In order to support passing stashes as arguments to _forgit_diff, we have to
     # prevent fzf from interpreting this substring by escaping the opening bracket.