fix travis builds by forcing it to ubuntu 14.04

This (for now) will force Travis' hand to use ubuntu 14.04 which has
mingw 4.8 available. It is enough to compile the project as it stands.

.travis.yml

@@ -17,3 +17,6 @@ cache:
     apt: true
 
 sudo: required
+
+services:
+    - docker

install.sh

@@ -74,6 +74,7 @@ if [[ `uname` == "Darwin" ]]; then
         popd
     fi
 elif [[ `uname` == "Linux" ]]; then
+	sudo apt-get update
 	if [[ -z "$TRAVIS" ]]; then
 	    sudo apt-get install -y binutils-mingw-w64-i686 gcc-mingw-w64-i686 g++-mingw-w64-i686 cmake
 		if [[ -z "$DISABLE_G2_BUILD" ]]; then