Relax the dependency bounds to newest compatible versions

Relax the dependency bounds in `setup.py` to permit the newest versions
that are compatible with the current httpbin code, that is permit
the test suite to pass.

setup.py

@@ -35,7 +35,7 @@
     packages=find_packages(),
     include_package_data = True, # include files listed in MANIFEST.in
     install_requires=[
-        'Flask<1.0.3', 'MarkupSafe<2.1', 'decorator', 'itsdangerous<2', 'brotlipy',
-        'raven[flask]', 'werkzeug==0.14.1', 'gevent', 'flasgger', 'jinja2==2.10'
+        'Flask<1.1', 'MarkupSafe<2.1', 'decorator', 'itsdangerous<2.1', 'brotlipy',
+        'raven[flask]', 'werkzeug<0.15', 'gevent', 'flasgger', 'jinja2<3.1'
     ],
 )