Remove unicode characters from requirements.txt.

[schmmd]

Some unicode characters were causing me trouble on a Linux machine, although not on a mac. I replaced them here with a space.

Previously:

# pip install -r requirements.txt 
Exception:
Traceback (most recent call last):
  File "/opt/conda/lib/python3.6/site-packages/pip/basecommand.py", line 215, in main
    status = self.run(options, args)
  File "/opt/conda/lib/python3.6/site-packages/pip/commands/install.py", line 312, in run
    wheel_cache
  File "/opt/conda/lib/python3.6/site-packages/pip/basecommand.py", line 295, in populate_requirement_set
    wheel_cache=wheel_cache):
  File "/opt/conda/lib/python3.6/site-packages/pip/req/req_file.py", line 84, in parse_requirements
    filename, comes_from=comes_from, session=session
  File "/opt/conda/lib/python3.6/site-packages/pip/download.py", line 422, in get_file_content
    content = auto_decode(f.read())
  File "/opt/conda/lib/python3.6/site-packages/pip/utils/encoding.py", line 31, in auto_decode
    return data.decode(locale.getpreferredencoding(False))
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc2 in position 590: ordinal not in range(128)

# git diff requirements.txt 
diff --git a/requirements.txt b/requirements.txt
index e131900..ea9c524 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -13,7 +13,7 @@ scikit-learn

 ## Tensorflow Requirements ##
 # Tensorflow is required to run this code but depends on specific configurations. Install from:
-#<C2><A0>https://www.tensorflow.org/get_started/os_setup#overview
+#   https://www.tensorflow.org/get_started/os_setup#overview
 # If you want to use the GPU version, you will also need Nvidia's CUDA toolkit and cuDNN:
 # https://developer.nvidia.com/cuda-downloads
 # https://developer.nvidia.com/cudnn