Make firefox with Sauce explicitly the default test

Apparently Travis-ci will create a default test separate from your
matrix includes and this resulted in some testrun duplication.

.travis.yml

@@ -7,6 +7,9 @@ env:
   - USE_SAUCE=true
   - NOKOGIRI_USE_SYSTEM_LIBRARIES=true
   - TEST_COMMAND="bash travis-core-script.sh"
+  - JASMINE_BROWSER="firefox"
+  - SAUCE_OS="Linux"
+  - SAUCE_BROWSER_VERSION=''
   - secure: WSPWhlnC4mWSnSPquX+m1/BCu5ch5NygkaHuM2Nea7lD8oS3XLX8QncZZAsQ4lnNfqoDDuBOizG0AESiqNvE4y6x5qvLLTS6q+ce255ZEMZ71TBdZgDEEvGMEjOPPsVXiXyTQOP1lwOPlrbZvaPgWV7e11KIBab6DfFcQpnvDgo=
   - secure: SW7CJhZnwaNT749Gdnhvqb5rbXlAOsygUAzh9qhtyvbqXKkmJdBIEsO01YF6pbju1X2twE9JvWCOxeZju43NgQChJlPsGbjY2j3k/TdQeTAJesQe2K7ytwghunI30gjEovtRH0T3w1EmcKPH8yj5eBIcB2OYoJHx8KEC7e68q1g=
 matrix:
@@ -14,11 +17,7 @@ matrix:
   - env:
     - USE_SAUCE=false
     - TEST_COMMAND="bash travis-node-script.sh"
-  - env: 
-    - JASMINE_BROWSER="firefox"
-    - SAUCE_OS="Linux"
-    - SAUCE_BROWSER_VERSION=''
-  - env: 
+  - env:
     - JASMINE_BROWSER="safari"
     - SAUCE_OS="OS X 10.8"
     - SAUCE_BROWSER_VERSION=6
@@ -26,22 +25,22 @@ matrix:
     - JASMINE_BROWSER="safari"
     - SAUCE_OS="OS X 10.6"
     - SAUCE_BROWSER_VERSION=5
-  - env: 
+  - env:
     - JASMINE_BROWSER="internet explorer"
     - SAUCE_OS="Windows 8"
     - SAUCE_BROWSER_VERSION=10
-  - env: 
+  - env:
     - JASMINE_BROWSER="internet explorer"
     - SAUCE_OS="Windows 7"
     - SAUCE_BROWSER_VERSION=9
-  - env: 
+  - env:
     - JASMINE_BROWSER="internet explorer"
     - SAUCE_OS="Windows 7"
     - SAUCE_BROWSER_VERSION=8
-  - env: 
+  - env:
     - JASMINE_BROWSER="chrome"
     - SAUCE_OS="Linux"
     - SAUCE_BROWSER_VERSION=''
-  - env: 
+  - env:
     - JASMINE_BROWSER="phantomjs"
     - USE_SAUCE=false