Put commands on one line (#884)

Multi-lines aren't supported this way in YAML. See https://yaml-multiline.info/.

Furthermore, the following **isn't supported** in our YAML DSL:

```
deploy:
  provider: script
  script:
    - command_1
    - command_2
```

Commands must be **on one line**:

```
deploy:
  provider: script
  script: command_1 && command_2
```

Otherwise, the best suggestion would be to put your commands **in an external script**:

```
deploy:
  provider: script
  script: ./external-script.sh
```

.travis.yml

@@ -33,23 +33,15 @@ matrix:
       deploy:
         provider: script
         skip_cleanup: true
-        script:
-          - AWS_ACCESS_KEY_ID=$AWS_915001051872_ID
-            AWS_SECRET_ACCESS_KEY=$AWS_915001051872_SECRET
-            ./deploy.sh -d
+        script: AWS_ACCESS_KEY_ID=$AWS_915001051872_ID AWS_SECRET_ACCESS_KEY=$AWS_915001051872_SECRET ./deploy.sh -d
         on:
           tags: true
     - env: DEPLOY=prod
       if: tag IS present
       deploy:
         provider: script
         skip_cleanup: true
-        script:
-          - AWS_ACCESS_KEY_ID=$AWS_192458993663_ID
-            AWS_SECRET_ACCESS_KEY=$AWS_192458993663_SECRET
-            ./deploy.sh -p
-          - AWS_ACCESS_KEY_ID=$AWS_192458993663_ID AWS_SECRET_ACCESS_KEY=$AWS_192458993663_SECRET aws cloudfront create-invalidation
-            --distribution-id E173XT6X8V4A18 --paths '/*'
+        script: AWS_ACCESS_KEY_ID=$AWS_192458993663_ID AWS_SECRET_ACCESS_KEY=$AWS_192458993663_SECRET ./deploy.sh -p && AWS_ACCESS_KEY_ID=$AWS_192458993663_ID AWS_SECRET_ACCESS_KEY=$AWS_192458993663_SECRET aws cloudfront create-invalidation --distribution-id E173XT6X8V4A18 --paths '/*'
         on:
           tags: true