also don't build memory-models.dir and clobber.dir

Author: Daniel Kroening

.travis.yml

@@ -41,4 +41,4 @@ matrix:
 script:
   - make -C src minisat2-download
   - make -C src CXX=$COMPILER CXXFLAGS="-Wall -O2 -g -Werror -Wno-deprecated-register -pedantic -Wno-sign-compare" -j2 && make -C regression test
-  - make -C src CXX=$COMPILER CXXFLAGS="-Wall -O2 -g -Werror -Wno-deprecated-register -pedantic -Wno-sign-compare" -j2 cegis.dir clobber.dir memory-models.dir musketeer.dir
+  - make -C src CXX=$COMPILER CXXFLAGS="-Wall -O2 -g -Werror -Wno-deprecated-register -pedantic -Wno-sign-compare" -j2 cegis.dir musketeer.dir