Travis: remove 3.3 tests, as it's EOL

Author: xoviat

.travis.yml

@@ -33,7 +33,6 @@ env:
   # Release builds:
   - PYTHON_VERSION="2.7" BUILD_SHARED_LIBS="yes"
   - PYTHON_VERSION="2.7" WITH_MPFR="yes" INTEGER_CLASS="gmpxx" WITH_NUMPY="no"
-  - PYTHON_VERSION="3.3" WITH_MPC="yes"
   - PYTHON_VERSION="3.4" WITH_MPFR="yes"
   - PYTHON_VERSION="3.5" WITH_MPC="yes"
   - PYTHON_VERSION="3.6" WITH_MPC="yes" INTEGER_CLASS="flint" WITH_FLINT="yes"