build: use the gcc-arm-embedded provided PPA instead of the tarball.

This makes the Travis configuration a little bit simpler and, as a
bonus, automatically uses the latest release of GCC to build
Cleanflight.

Signed-off-by: Michael Hope <mlhx@google.com>

.travis.yml

@@ -22,14 +22,10 @@ language: cpp
 compiler: clang
 
 before_install:
-  - sudo apt-get update
-  - wget "https://launchpad.net/gcc-arm-embedded/4.8/4.8-2014-q3-update/+download/gcc-arm-none-eabi-4_8-2014q3-20140805-linux.tar.bz2"
+  - sudo add-apt-repository -y ppa:terry.guo/gcc-arm-embedded
+  - sudo apt-get -qq update
+  - sudo apt-get -qq install gcc-arm-none-eabi
 
-install: 
-  - sudo apt-get install build-essential git libc6-i386
-  - tar -xf gcc-arm-none-eabi-4_8-2014q3-20140805-linux.tar.bz2
-  - export PATH=$PATH:$PWD/gcc-arm-none-eabi-4_8-2014q3/bin
-   
 before_script: arm-none-eabi-gcc --version
 script: ./.travis.sh