Run Prettier first on CI

Fixes some edge case where Prettier doesn't take .gitignore into account
and lints against some files under .vscode-test/ (Windows only...?)

Author: Xanewok

.gitignore

@@ -1,4 +1,4 @@
 out
 node_modules
-.vscode-test/
+.vscode-test
 *.vsix

.travis.yml

@@ -25,7 +25,7 @@ before_install:
   - export PATH="$HOME/.cargo/bin:$PATH"
 
 script:
+  - npm run prettier -- --list-different
   - npm run compile
-  - npm run test
   - npm run lint
-  - npm run prettier -- --list-different
+  - npm run test