Update docker util script and travis to use new base container

Dockerfile

@@ -1,9 +1,5 @@
 FROM qmkfm/base_container
 
-# upgrade gcc-arm-none-eabi from the default 5.4.1 to 6.3.1 due to ARM runtime issues
-RUN wget -q https://developer.arm.com/-/media/Files/downloads/gnu-rm/6-2017q2/gcc-arm-none-eabi-6-2017-q2-update-linux.tar.bz2 -O - | \
-    tar xj --strip-components=1 -C /
-
 VOLUME /qmk_firmware
 WORKDIR /qmk_firmware
 COPY . .