#310 Support spaces in filename

The spec does not state if spaces are supported. The previous code will
throw the following critical error if space is detected in file name:
```
CRITICAL: Invalid characters '  ' in file name at: 
```

This commit add ' ' as a valid character.

Signed-off-by: Chin Yeung Li <tli@nexb.com>

Author: chinyeungli

src/attributecode/util.py

@@ -68,7 +68,7 @@ def to_posix(path):
 UNC_PREFIX_POSIX = to_posix(UNC_PREFIX)
 UNC_PREFIXES = (UNC_PREFIX_POSIX, UNC_PREFIX,)
 
-valid_file_chars = string.digits + string.ascii_letters + '_-.'
+valid_file_chars = string.digits + string.ascii_letters + '_-.' + ' '
 
 
 def invalid_chars(path):

tests/test_util.py

@@ -171,6 +171,11 @@ def test_invalid_chars_with_valid_chars(self):
         expected = []
         assert expected == result
 
+    def test_space_is_valid_chars(self):
+        result = util.invalid_chars(' ')
+        expected = []
+        assert expected == result
+
     def test_invalid_chars_with_invalid_in_name_and_dir(self):
         result = util.invalid_chars('_$as/afg:')
         expected = [':']