Do not install yarn on Travis

Yarn is already installed on Travis and does not needed to added.

.travis.yml

@@ -32,7 +32,9 @@ matrix:
   fast_finish: true
 
 install:
-  - bash ./ci/travis-install.sh
+  - yarn --frozen-lockfile
+  - yarn link --frozen-lockfile || true
+  - yarn link webpack --frozen-lockfile
 
 script: npm run travis:$JOB_PART
 

ci/travis-install.sh

@@ -1,12 +0,0 @@
-#!/bin/bash
-set -ev
-
-curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.0.1
-
-export PATH=$HOME/.yarn/bin:$PATH
-
-yarn link --frozen-lockfile || true;
-
-yarn --frozen-lockfile
-
-yarn link webpack --frozen-lockfile