Set correct file encoding for Windows

[FriedrichFroebel]

This fixes the blocks test by setting the UTF-8 encoding when opening the JSON file. Otherwise the corresponding test may fail on Windows because the default encoding (in my case CP-1252) is used which cannot handle some of the characters:

======================================================================
ERROR: Parse locally stored grid and compare to expected results
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Python\lib\unittest\mock.py", line 1195, in patched
    return func(*args, **keywargs)
  File "C:\Me\GitHub\pycaching\test\test_geo.py", line 207, in test_blocks
    mock_utfgrid.return_value = json.load(f)
  File "C:\Python\lib\json\__init__.py", line 293, in load
    return loads(fp.read(),
  File "C:\Python\lib\encodings\cp1252.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
UnicodeDecodeError: 'charmap' codec can't decode byte 0x81 in position 1346: character maps to <undefined>

[tomasbedrich]

What a noob mistake. :) Thanks!