[travis] Disable testing of Octave bindings in master

For some reason, Octave tests started failing in master. 
Given that we will soon merge `devel` in `master` and in the `devel` the bindings for Octave changed completely (see #305),  I think for the time being we can just disable testing the Octave bindings in master.

.travis.yml

@@ -60,7 +60,7 @@ before_script:
   - mkdir build
   - cd build
   # Xcode has support for multiple configurations. Passing -DCMAKE_BUILD_TYPE is ignored
-  - cmake -G"${TRAVIS_CMAKE_GENERATOR}" -DCMAKE_BUILD_TYPE=${TRAVIS_BUILD_TYPE} -DIDYNTREE_COMPILE_TESTS:BOOL=ON -DIDYNTREE_RUN_VALGRIND_TESTS:BOOL=${VALGRIND_TESTS} -DCODYCO_TRAVIS_CI:BOOL=ON -DIDYNTREE_USES_PYTHON:BOOL=${COMPILE_BINDINGS} -DIDYNTREE_USES_LUA:BOOL=${COMPILE_BINDINGS} -DIDYNTREE_USES_OCTAVE:BOOL=${COMPILE_BINDINGS} ..
+  - cmake -G"${TRAVIS_CMAKE_GENERATOR}" -DCMAKE_BUILD_TYPE=${TRAVIS_BUILD_TYPE} -DIDYNTREE_COMPILE_TESTS:BOOL=ON -DIDYNTREE_RUN_VALGRIND_TESTS:BOOL=${VALGRIND_TESTS} -DCODYCO_TRAVIS_CI:BOOL=ON -DIDYNTREE_USES_PYTHON:BOOL=${COMPILE_BINDINGS} -DIDYNTREE_USES_LUA:BOOL=${COMPILE_BINDINGS} -DIDYNTREE_USES_OCTAVE:BOOL=OFF ..
 
 script:
   - cmake --build . --config ${TRAVIS_BUILD_TYPE}