Using arithmetic brackets for numerical comparison, instead of conditional brackets.

Using == with [[ is a string comparison, not a numerical comparison as it ought
to be.

themes/giddie/prompt_giddie_setup

@@ -24,7 +24,7 @@ function prompt_giddie_precmd {
 
   # Choose prompt symbol based on whether on not we're in a repository.
   { git branch 2>&1 } >/dev/null
-  if [[ $? == 0 ]]; then
+  if (( $? == 0 )); then
     prompt_symbol='±'
   else
     prompt_symbol=')'