workaround Travis javadoc build

Author: mikesamuel

scripts/build_for_travis.sh

@@ -15,9 +15,7 @@ if echo $TRAVIS_JDK_VERSION | egrep -q '(jdk|jre)[67]($|[^0-9])'; then
     # but Guava 21.0 is compatibility with jdk 7.
     COMMON_FLAGS="$COMMON_FLAGS -Dguava.version=20.0"
 fi
-if echo $TRAVIS_JDK_VERSION | egrep -q '(jdk|jre)9($|[^0-9])'; then
-  ;
-else
+if ! echo $TRAVIS_JDK_VERSION | egrep -q '(jdk|jre)9($|[^0-9])'; then
     # Older versions of javadoc barf on -Xdoclint flags used
     # to configure the maven-javadoc-plugin.
     # TODO: Newer versions barf on modules for some reason.