Use npm i shorthand in .travis.yml. [ci skip]

.travis.yml

@@ -40,7 +40,7 @@ branches:
   only:
     - master
 before_install:
-  - "[ $BIN == 'istanbul' ] && npm install -g istanbul || true"
+  - "[ $BIN == 'istanbul' ] && npm i -g istanbul || true"
   - "[ $BIN == 'narwhal' ] && wget https://github.com/280north/narwhal/archive/v0.3.2.zip && sudo unzip v0.3.2 -d /opt/ && rm v0.3.2.zip || true"
   - "[ $BIN == 'narwhal' ] && sudo ln -s /opt/narwhal-0.3.2/bin/narwhal /usr/local/bin/narwhal && sudo chmod +x /usr/local/bin/narwhal || true"
   - "[ $BIN == 'rhino' ] && sudo mkdir /opt/rhino-1.7R5 && sudo wget -O /opt/rhino-1.7R5/js.jar https://oss.sonatype.org/content/repositories/snapshots/org/mozilla/rhino/1.7R5-SNAPSHOT/rhino-1.7R5-20120629.144839-4.jar || true"