Don't use urandom for the upload data source

Using urandom limits the upload speed due to the generation speed of
random characters and causes high CPU usage.

See #13
Fixes #26

setup.py

@@ -4,7 +4,7 @@ import setuptools
 
 setuptools.setup(
     name='speedtest-cli',
-    version='0.2',
+    version='0.2.1',
     description=('Command line interface for testing internet bandwidth using '
                  'speedtest.net'),
     author='Matt Martz',