Change `npm install` to `npm ci` so lock file is not updated

.travis.yml

@@ -4,7 +4,7 @@ language:
 
 install:
   - bundle install
-  - npm install
+  - npm ci
 
 script:
   - npm run build

README.md

@@ -78,7 +78,7 @@ to the `dependencies` in your `component.json`.
 From the root of the repository, install the tools used to develop.
 
     $ bundle install
-    $ npm install
+    $ npm ci
 
 Build the font:
 

src/doc/README.md-nobuild

@@ -80,7 +80,7 @@ to the `dependencies` in your `component.json`.
 From the root of the repository, install the tools used to develop.
 
     $ bundle install
-    $ npm install
+    $ npm ci
 
 Build the font: