[FIX] build: call make explicitely, as it is not implied in make vtest

1 job from master in 53 minutes 30 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #402
buildAndTest

53:30

 
WGETextureHud.cpp:(.text+0x1bba): undefined reference to `osgText::TextBase::setText(std::string const&)'
collect2: error: ld returned 1 exit status
core/CMakeFiles/openwalnut.dir/build.make:8603: recipe for target 'lib/libopenwalnut.so.1.5.0' failed
make[2]: *** [lib/libopenwalnut.so.1.5.0] Error 1
CMakeFiles/Makefile2:879: recipe for target 'core/CMakeFiles/openwalnut.dir/all' failed
make[1]: *** [core/CMakeFiles/openwalnut.dir/all] Error 2
Makefile:127: recipe for target 'all' failed
make: *** [all] Error 2
ERROR: Job failed: exit status 1