Use Travis matrix with TOOLSET env spec.

.travis.yml

@@ -1,8 +1,5 @@
 language: cpp
 
-compiler:
-  - gcc
-
 branches:
   only:
     - develop
@@ -24,16 +21,15 @@ notifications:
 os:
   - linux
 
+matrix:
+  include:
+    - compiler: gcc
+      env: TOOLSET=gcc-4.7
+
 before_install: wget "https://raw.githubusercontent.com/boostorg/regression/develop/ci/src/script.py"
-
 install: python script.py travis_install
-
 before_script: python script.py travis_before_script
-
 script: python script.py travis_script
-
 after_success: python script.py travis_after_success
-
 after_failure: python script.py travis_after_failure
-
 after_script: python script.py travis_after_script