Don't try to decrypt with variables that don't exist

Author: bhstahl

.travis.yml

@@ -4,7 +4,7 @@ node_js:
   - "6.0"
 
 before_install:
-  - openssl aes-256-cbc -K $encrypted_d9f08a58d46a_key -iv $encrypted_d9f08a58d46a_iv -in keyfile.json.enc -out keyfile.json -d
+  - 'if [ "$TRAVIS_SECURE_ENV_VARS" != "false" ]; then openssl aes-256-cbc -K $encrypted_d9f08a58d46a_key -iv $encrypted_d9f08a58d46a_iv -in keyfile.json.enc -out keyfile.json -d; fi'
 
 script:
   - npm run lint