Switch package management from npm to yarn

.travis.yml

@@ -1,7 +1,5 @@
 language: node_js
-cache:
-  directories:
-    - node_modules
+cache: yarn
 notifications:
   slack:
     rooms:
@@ -11,9 +9,9 @@ matrix:
     # 'node_js' is listed for each job to ensure that only two builds are run.
     # See https://github.com/hypothesis/client/pull/27#discussion_r70611726
     - env: ACTION=lint
-      node_js: '6.2'
-      script: npm run lint
+      node_js: '6.10'
+      script: yarn run lint
     - env: ACTION=test
-      node_js: '6.2'
+      node_js: '6.10'
       after_success:
-        npm run report-coverage
+        yarn run report-coverage

Jenkinsfile

@@ -3,7 +3,7 @@
 node {
     checkout scm
 
-    nodeEnv = docker.image("node:6.2")
+    nodeEnv = docker.image("kkarczmarczyk/node-yarn:7.5")
     workspace = pwd()
 
     stage 'Build'
@@ -24,7 +24,7 @@ node {
                 [$class: 'StringBinding', credentialsId: 'npm-token', variable: 'NPM_TOKEN']]) {
 
                 sh "echo '//registry.npmjs.org/:_authToken=${env.NPM_TOKEN}' >> \$HOME/.npmrc"
-                sh "npm publish"
+                sh "yarn publish"
             }
         }
 

Makefile

@@ -13,11 +13,11 @@ clean:
 ## Run test suite
 .PHONY: test
 test: node_modules/.uptodate
-	npm test
+	yarn test
 
 .PHONY: lint
 lint: node_modules/.uptodate
-	npm run lint
+	yarn run lint
 
 .PHONY: docs
 docs:
@@ -26,8 +26,8 @@ docs:
 ################################################################################
 
 build/manifest.json: node_modules/.uptodate
-	npm run-script build
+	yarn run build
 
-node_modules/.uptodate: package.json npm-shrinkwrap.json
-	npm run-script deps 2>/dev/null || npm install
+node_modules/.uptodate: package.json yarn.lock
+	yarn run deps 2>/dev/null || yarn install
 	@touch $@

docs/developers/developing.rst

@@ -14,7 +14,8 @@ Prerequisites
 You will need:
 
 * `git <https://git-scm.com/>`_
-* `Node.js <https://nodejs.org/en/>`_ v6+
+* `Node.js <https://nodejs.org/en/>`_ v6.3+
+* `Yarn <https://yarnpkg.com/lang/en/>`_
 
 Building
 ########