Pin and update PyFxA + PyPOM dependencies

* Update PyFxA dependency to 0.5.0

* Pin PyPOM and PyFxA to latest

requirements/py27-tests.txt

@@ -1,5 +1,7 @@
 mock==2.0.0
 mozlog==3.7
+pyfxa==0.5.0
+pypom==1.3.0
 pytest==3.4.2
 pytest-metadata==1.6.0
 pytest-selenium==1.12.0

requirements/py36-tests.txt

@@ -1,4 +1,6 @@
 mock==2.0.0
+pyfxa==0.5.0
+pypom==1.3.0
 pytest==3.4.2
 pytest-metadata==1.6.0
 pytest-selenium==1.12.0

setup.py

@@ -25,5 +25,5 @@ setup(name='fxapom',
       license='MPL 2.0',
       packages=find_packages(exclude=['ez_setup', 'examples', 'tests']),
       setup_requires=['setuptools_scm'],
-      install_requires=['PyFxA==0.4.0', 'PyPOM'],
+      install_requires=['PyFxA', 'PyPOM'],
       include_package_data=True)