[Tests] npm v4.6+ breaks in node < v1; npm 5+ breaks in node < v4

Author: ljharb

.travis.yml

@@ -9,8 +9,10 @@ env:
   - 'TEST_DIR=packages/eslint-config-airbnb-base'
 before_install:
   - 'cd $TEST_DIR'
-  - 'if [ "${TRAVIS_NODE_VERSION}" != "0.9" ]; then case "$(npm --version)" in 1.*) npm install -g npm@1.4.28 ;; 2.*) npm install -g npm@2 ;; esac ; fi'
-  - 'if [ "${TRAVIS_NODE_VERSION}" != "0.6" ] && [ "${TRAVIS_NODE_VERSION}" != "0.9" ]; then npm install -g npm; fi'
+  - 'if [ "${TRAVIS_NODE_VERSION}" = "0.6" ]; then npm install -g npm@1.3 ; elif [ "${TRAVIS_NODE_VERSION}" != "0.9" ]; then case "$(npm --version)" in 1.*) npm install -g npm@1.4.28 ;; 2.*) npm install -g npm@2 ;; esac ; fi'
+  - 'if [ "${TRAVIS_NODE_VERSION%${TRAVIS_NODE_VERSION#[0-9]}}" = "0" ] || [ "${TRAVIS_NODE_VERSION:0:4}" = "iojs" ]; then npm install -g npm@4.5 ; elif [ "${TRAVIS_NODE_VERSION}" != "0.6" ] && [ "${TRAVIS_NODE_VERSION}" != "0.9" ]; then npm install -g npm; fi'
+install:
+  - 'if [ "${TRAVIS_NODE_VERSION}" = "0.6" ]; then nvm install 0.8 && npm install -g npm@1.3 && npm install -g npm@1.4.28 && npm install -g npm@2 && npm install && nvm use "${TRAVIS_NODE_VERSION}"; else npm install; fi;'
 script:
   - 'npm run travis'
 sudo: false