Container's not flexible enough, back to the old approach.

.travis.yml

@@ -1,11 +1,16 @@
-sudo: false
+# sudo: false
 
 language: cpp
 
-addons:
+# addons:
-  apt:
+#   apt:
-    packages:
+#     packages:
-      - gcc-arm-none-eabi
+#       - gcc-arm-none-eabi
+
+before_script:
+  - sudo add-apt-repository ppa:terry.guo/gcc-arm-embedded -y
+  - sudo apt-get update -qq
+  - sudo apt-get install -y gcc-arm-none-eabi
 
 script:
   - cd firmware/