Fix travis script to force delete

In case the file does not exist the failure to delete will not cause build to flag as FAILED.

Author: minbi

.travis.yml

@@ -10,7 +10,7 @@ android:
     - android-15
 sudo: true
 script:
-    - sudo rm /etc/mavenrc
+    - sudo rm -f /etc/mavenrc
     - export MAVEN_OPTS="-Xms512m -Xmx1024m -XX:PermSize=256m -XX:MaxPermSize=512m"
     - mvn clean install -Dmaven.javadoc.skip=true cobertura:cobertura