Quick fix for Travis CI: remove signed-off check

Pull requests creating merge commits don't work well with
tools/check-signed-off.sh.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss [email protected]

Author: akosthekiss

.travis.yml

@@ -13,7 +13,7 @@ install: make prerequisites
 script: "make -j VERBOSE=1 NINJA=1 $TARGET"
 
 env:
-  - TARGET="check-signed-off check-vera check-cpp"
+  - TARGET="check-vera check-cpp"
   - TARGET="build.linux test-js-precommit"
   - TARGET=build.mcu_stm32f3
   - TARGET=build.mcu_stm32f4