fix wercker.yml (trigger-crowi-plus-docker)

wercker.yml

@@ -81,8 +81,8 @@ release: # would be run on release branch
         # npm version to bump version
         npm version patch
         # get version
-        RELEASE_VERSION=`npm run version --silent`
-        echo "RELEASE_VERSION=$RELEASE_VERSION"
+        export RELEASE_VERSION=`npm run version --silent`
+        echo "export RELEASE_VERSION=$RELEASE_VERSION"
 
     - script:
       name: commit and push