travis: Update travis script for clang and libusb-1.0

.travis.yml

@@ -1,10 +1,16 @@
 language: c
 compiler:
   - gcc
+  - clang
 before_install:
   - sudo apt-get update -qq
-  - sudo apt-get install -qq -y libusb-dev
+  - sudo apt-get install -qq -y libusb-1.0-0-dev
-script: if [ ${COVERITY_SCAN_BRANCH} != 1 ]; then make ; fi
+script: if [ "${COVERITY_SCAN_BRANCH}" != 1 ]; then make ; fi
+
+matrix:
+  exclude:
+    - compiler: clang
+    - env: COVERITY_SCAN_BRANCH=1
 
 env:
   global:
@@ -16,5 +22,5 @@ addons:
       name: "pali/0xFFFF"
       description: "Build submitted via Travis CI"
     notification_email: pali.rohar@gmail.com
-    build_command: "make"
+    build_command: make
     branch_pattern: master