use gcc 4.8 for build

.travis.yml

@@ -1,12 +1,17 @@
+addons:
+    apt:
+        sources:
+            - ubuntu-toolchain-r-test
+        packages:
+            - g++-4.8
+            - gcc-4.8
 before_install:
     - sudo apt-get update -qq
     - sudo apt-get install -y libwxgtk3.0-dev libgtk2.0-dev
     - git show -s --format="wxT(\"<a href=\\\"http://github.com/audacity/audacity/commit/%H\\\">%h</a> of %cd\")"
     - git show -s --format="wxT(\"<a href=\\\"http://github.com/audacity/audacity/commit/%H\\\">%h</a> of %cd\")" > ./src/RevisionIdent.h
+    - export CXX="g++-4.8" CC="gcc-4.8"
 language:
     - cpp
-compiler:
-    - gcc
-script: 
+script:
     - aclocal --install -I m4 && automake && ./configure && make
-