Use double bracket bash conditional per style guide

servo · aneeshusa · Apr 12, 2017 · Apr 12, 2017 · Apr 12, 2017 · May 6, 2017
commit c8689204ddef07f7632f4eeeb916300062221084
diff --git a/.travis/dispatch.sh b/.travis/dispatch.sh
@@ -86,7 +86,7 @@ elif [[ -n "${SALT_DOCKER_IMAGE:-}" ]]; then  # macOS bash is too old for `-v`
 
     run_inside_docker "$@"
 else
-    if [ "${SALT_FROM_SCRATCH}" = "true" ]; then
+    if [[ "${SALT_FROM_SCRATCH}" = "true" ]]; then
         run_salt 'scratch'
     else
         git fetch origin master:master