Fix compile fail for GIT version

.travis.yml

@@ -128,6 +128,8 @@ after_success:
       && echo https://px4-travis.s3.amazonaws.com/archives/Firmware/$TRAVIS_BRANCH/$TRAVIS_BUILD_ID/Firmware.zip
       ;
     fi
+  - git log -n 1 --pretty=format:"%H"
+  - git rev-parse HEAD
 
 deploy:
   provider: releases

cmake/common/px4_base.cmake

@@ -700,7 +700,7 @@ function(px4_create_git_hash_header)
 		REQUIRED HEADER 
 		ARGN ${ARGN})
 	execute_process(
-		COMMAND git rev-parse HEAD
+		COMMAND git log -n 1 --pretty=format:"%H"
 		OUTPUT_VARIABLE git_desc
 		OUTPUT_STRIP_TRAILING_WHITESPACE
 		WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}