Corrected __init__ call for SyntaxCorpusReader subclasses

[tomaarsen]

Resolves #2118

Hello!

Pull request overview

• Replaced CorpusReader.__init__(...) with SyntaxCorpusReader.__init__(...) on classes that inherit from SyntaxCorpusReader.

Details

See #2118 for details on the issue.

Beyond that:

>>> 
>>> from nltk.corpus import CorpusReader, SyntaxCorpusReader
>>> CorpusReader.__init__ == SyntaxCorpusReader.__init__
True

SyntaxCorpusReader inherits from CorpusReader, and the former doesn't specify a __init__, so both methods are identical. That means, we can just go for the logical option of calling __init__ on the parent we are actually inheriting from.

• Tom Aarsen