quadratic operator docs errors

[aaronmarkham]

Description

Sphinx throws errors when generating the docs for the quadratic op.

Error

/home/ubuntu/incubator-mxnet/python/mxnet/ndarray/contrib.py:docstring of mxnet.ndarray.contrib.quadratic:3: ERROR: Unexpected indentation.
/home/ubuntu/incubator-mxnet/python/mxnet/ndarray/contrib.py:docstring of mxnet.ndarray.contrib.quadratic:4: WARNING: Literal block ends without a blank line; unexpected unindent.
/home/ubuntu/incubator-mxnet/python/mxnet/ndarray/contrib.py:docstring of mxnet.ndarray.contrib.quadratic:7: ERROR: Unexpected indentation.

[frankfliu]

@mxnet-label-bot [Doc]