travis: Fix error reporting on failed builds

Apparently after_script is allowed to fail, so just
run the tests inside script.

.travis.yml

@@ -61,7 +61,6 @@ script:
 - cmake -DHAVE_GTK2=NO -DBUILD_METALIBS=$BUILD_METALIBS -DCOMPOSITE_SOURCE_LIMIT=$COMPOSITE_SOURCE_LIMIT .. 
 - make -j4
 
-after_script:
 - python ../test_imports.py
 - pytest ../tests