Fix error in customer testing script.

There was an error in the bash script running the customer tests.

Change-Id: If6414fcaf221372e51727c3f9a4962182dbcd0cc
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/25920
Reviewed-by: Kevin Chisholm <kevinjchisholm@google.com>
Reviewed-by: Casey Hillers <chillers@google.com>
Commit-Queue: Godofredo Contreras <godofredoc@google.com>
diff --git a/recipe_modules/adhoc_validation/resources/customer_testing.sh b/recipe_modules/adhoc_validation/resources/customer_testing.sh
index 8e4106d..5dbf91b 100644
--- a/recipe_modules/adhoc_validation/resources/customer_testing.sh
+++ b/recipe_modules/adhoc_validation/resources/customer_testing.sh
@@ -8,7 +8,7 @@
 
 # Customer testing require both master and the branch
 # under test to be checkout out.
-if [$GIT_BRANCH != 'master']
+if [ "$GIT_BRANCH" != 'master' ]
 then
   git fetch origin master
   git checkout master