[ci] Update ARM GCC to 6.1 2017q1.

It does not crash anymore with LPC linker files.

.travis.dep.sh

@@ -37,9 +37,9 @@ if [ ! -d "$HOME/cache/avr8-gnu-toolchain-linux_x86" ]; then
 	tar -xzf avr8.tar.gz
 	rm avr8.tar.gz
 fi
-if [ ! -d "$HOME/cache/gcc-arm-none-eabi-4_9-2015q3" ]; then
+if [ ! -d "$HOME/cache/gcc-arm-none-eabi-6-2017-q1-update" ]; then
 	echo "Downloading Cortex-M toolchain..."
-	wget https://launchpad.net/gcc-arm-embedded/4.9/4.9-2015-q3-update/+download/gcc-arm-none-eabi-4_9-2015q3-20150921-linux.tar.bz2 -O cortex_m.tar.bz2
+	wget https://developer.arm.com/-/media/Files/downloads/gnu-rm/6_1-2017q1/gcc-arm-none-eabi-6-2017-q1-update-linux.tar.bz2 -O cortex_m.tar.bz2
 	tar -xjf cortex_m.tar.bz2
 	rm cortex_m.tar.bz2
 fi

.travis.yml

@@ -25,10 +25,10 @@ before_install:
  - export LD_LIBRARY_PATH="$HOME/cache/boost/lib:$LD_LIBRARY_PATH"
  - export CXXFLAGS="-isystem$HOME/cache/boost/include"
  - export LDFLAGS="-L$HOME/cache/boost/lib"
- - export PATH="$HOME/cache/avr8-gnu-toolchain-linux_x86/bin:$HOME/cache/gcc-arm-none-eabi-4_9-2015q3/bin:$PATH"
+ - export PATH="$HOME/cache/avr8-gnu-toolchain-linux_x86/bin:$HOME/cache/gcc-arm-none-eabi-6-2017-q1-update/bin:$PATH"
  - echo $PATH
  - ls -l $HOME/cache/avr8-gnu-toolchain-linux_x86/bin
- - ls -l $HOME/cache/gcc-arm-none-eabi-4_9-2015q3/bin
+ - ls -l $HOME/cache/gcc-arm-none-eabi-6-2017-q1-update/bin
  - ls -l $HOME/cache/boost
  - which avr-g++
  - avr-g++ --version