CI: Fixing setting up job-specific environment variables

.travis.yml

@@ -21,8 +21,7 @@ jobs:
     - stage: pre-build
       script: skip
     - stage: build
-      script: ./bin/build-site.sh
-      env:
-        - TW5_BUILD_TIDDLYWIKI = ./node_modules/tiddlywiki/tiddlywiki.js
+      script: TW5_BUILD_TIDDLYWIKI='./node_modules/tiddlywiki/tiddlywiki.js' && \
+        ./bin/build-site.sh
     - stage: deploy
       script: ./bin/deploy-site.sh