fix typo in docker test script (#10334)

share/spack/qa/run-docker-tests

@@ -37,7 +37,7 @@ for config in share/spack/docker/config/* ; do
     ./share/spack/docker/build-image.sh;
 done
 
-if [ "$TEST_SUITE" '=' "docker build" -a \
+if [ "$TEST_SUITE" '=' "docker" -a \
      "$TRAVIS_EVENT_TYPE" != "pull_request" -a \
      ensure_docker_login ] ; then