change shebang to more universal shebang

src/rmi_splitter/__init__.py

src/rmi_splitter/rmi_splitter.py

src/rmi_splitter/suffix_tree.py

src/rmi_splitter/tests/__init__.py

src/rmi_splitter/tests/data_test.py

src/rmi_splitter/tests/rmi_splitter_test.py

src/rmi_splitter/tests/suffix_tree_test.py

src/setup.py