update publish.sh for changes in repo structure (#65)

diff --git a/tools/travis/publish.sh b/tools/travis/publish.sh
index 82a6adb..c93cebe 100755
--- a/tools/travis/publish.sh
+++ b/tools/travis/publish.sh
@@ -42,7 +42,7 @@
 
 if [[ ! -z ${RUNTIME} ]]; then
 TERM=dumb ./gradlew \
-:${RUNTIME}:distDocker \
+core:${RUNTIME}:distDocker \
 -PdockerRegistry=docker.io \
 -PdockerImagePrefix=${IMAGE_PREFIX} \
 -PdockerImageTag=${IMAGE_TAG}