Fix improper use of == with [

`==` is only (semi-)portable when used with `[[`.

Author: MPLew-is

gitprompt.sh

@@ -713,12 +713,12 @@ function add_prompt_command() {
     return 0
   fi
 
-  if [ -z "$PROMPT_COMMAND" ]; then
+  if [[ -z "$PROMPT_COMMAND" ]]; then
     PROMPT_COMMAND="$new_entry"
     return 0
   fi
 
-  if [ "$insert_before" == "true" ]; then
+  if [[ "$insert_before" == "true" ]]; then
     PROMPT_COMMAND="${new_entry};${PROMPT_COMMAND}"
   else
     PROMPT_COMMAND="${PROMPT_COMMAND};${new_entry}"

tests/test-non-git-ps1.sh

@@ -23,7 +23,7 @@ function test_original_prompt_is_restored() {
   # Navigate back into the repo
   cd "$REPO_ROOT"
   run_prompt_command
-  if [ "$PS1" == "$" ]; then
+  if [[ "$PS1" == "$" ]]; then
     echo "PS1: $PS1 == \$"
     return 1
   fi