Combine and extract before_install

.travis.yml

@@ -3,7 +3,8 @@ language: rust
 sudo: required
 
 before_install:
-  git clone https://github.com/eldruin/rust-driver-ci-scripts ci
+  - git clone https://github.com/eldruin/rust-driver-ci-scripts ci
+  - bash ci/before_install.sh
 
 matrix:
   include:
@@ -49,10 +50,6 @@ matrix:
     - env: TARGET=thumbv7m-none-eabi
       rust: beta
 
-before_install:
-  - set -e
-  - rustup self update
-
 install:
   bash ci/install.sh