Fix dev-requirements for towncrier.

dev-requirements.txt

@@ -7,11 +7,10 @@ pylint>=1.8.0 ; python_version < "3.4"
 # pylint 2 needs astroid 2; unfortunately, it uses `typed_ast`
 # which has a C extension that doesn't build on PyPy
 pylint >= 2.3.1 ; python_version >= "3.4"  and platform_python_implementation == "CPython"
-astroid >= 2.2.5 ; python_version >= "3.4" and
-platform_python_implementation == "CPython"
+astroid >= 2.2.5 ; python_version >= "3.4" and platform_python_implementation == "CPython"
 
 # For generating CHANGES.rst
-towncrier; python_version >= 3.5
+towncrier
 
 # benchmarks use this
 pyperf >= 1.6.1