fix(travis): install/use g++-4.8 for node 4.x build of scrypt-hash

.travis.yml

@@ -8,13 +8,23 @@ env:
 node_js:
  - "0.10"
  - "0.12"
- - "iojs-v2"
+ - "4"
 
 sudo: false
 
+addons:
+  apt:
+    sources:
+    - ubuntu-toolchain-r-test
+    packages:
+    - g++-4.8
+
 env:
-  - NODE_ENV=test DB=memory
-  - NODE_ENV=test DB=mysql
+  global:
+    - NODE_ENV=test
+  matrix:
+    - DB=memory
+    - DB=mysql
 
 notifications:
   email:
@@ -33,6 +43,10 @@ before_install:
   - npm install -g npm@2
   - npm config set spin false
 
+install:
+  # use c++-11 with node4, default compiler on downlevel versions
+  - if [ $TRAVIS_NODE_VERSION == "4" ]; then CXX=g++-4.8 npm install; else npm install; fi
+
 script:
   - if [ $DB == "mysql" ]; then ./scripts/start-travis-auth-db-mysql.sh; fi
   - npm test