Remove unnecesary before_install step

.travis.yml

@@ -4,13 +4,9 @@ cache:
     directories:
         - node_modules
 addons:
-    chrome: stable
+  chrome: unstable
 node_js:
  - "10"
-before_install:
-  - npm install -g lerna
-  - rm -rf ./node_modules
-  - export LERNA=$(which lerna)
 install: make stamp-npm
 before_script: make serve_bg
 script: make check