travis: Drop conditional on Linux

We currently run CI on Linux only, given that the macOS builders in
Travis are always fairly overwhelmed; thus, there's no need to
complicate the Travis script with a conditional that is always going to
be true.

.travis.yml

@@ -19,14 +19,14 @@ services:
   - docker
 
 before_install:
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then docker pull ebassi/epoxyci ; fi
+  - docker pull ebassi/epoxyci
 
 before_script:
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then echo FROM ebassi/epoxyci > Dockerfile ; fi
+  - echo FROM ebassi/epoxyci > Dockerfile
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then echo ADD . /root >> Dockerfile ; fi
+  - echo ADD . /root >> Dockerfile
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then docker build -t withgit . ; fi
+  - docker build -t withgit .
 
 script:
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then docker run withgit /bin/sh -c "cd /root && CC=$CC ./epoxy-run-tests.sh" ; fi
+  - docker run withgit /bin/sh -c "cd /root && CC=$CC ./epoxy-run-tests.sh"
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then docker run withgit /bin/sh -c "cd /root && CC=$CC ./epoxy-run-tests.sh -Denable-glx=no" ; fi
+  - docker run withgit /bin/sh -c "cd /root && CC=$CC ./epoxy-run-tests.sh -Denable-glx=no"
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then docker run withgit /bin/sh -c "cd /root && CC=$CC ./epoxy-run-tests.sh -Denable-egl=no" ; fi
+  - docker run withgit /bin/sh -c "cd /root && CC=$CC ./epoxy-run-tests.sh -Denable-egl=no"