Fix string comparison in bump-version script (#1638)

The validation on line 9 used (( )) arithmetic context for string
comparison, which always errors. Replace with [[ ]] for proper string
matching and add || usage to actually reject invalid inputs.

Author: jeffwidman

script/bump-version

@@ -6,7 +6,7 @@ while getopts "p:" o; do
   case "${o}" in
     p)
       patch_level=${OPTARG}
-      (( patch_level == 'major' || patch_level == 'minor' || patch_level == 'patch'))
+      [[ "${patch_level}" == 'major' || "${patch_level}" == 'minor' || "${patch_level}" == 'patch' ]] || usage
       ;;
     *)
       usage