DOC: remove latex and parallel building
This seemed to work on my fork on travis, but not sure why removing the parallel would fix it. yep this looks good. fyi

not exactly sure what is wrong here :>
```
/tmp/doc/source/io.rst:3097: ERROR: Error in "ipython" directive:
invalid option block.
.. ipython:: python
   :suppress:
   import os
   os.remove("data.pkl.compress")
   os.remove("data.pkl.xz")
   os.remove("data.pkl.gz")
   os.remove("s1.pkl.bz2")
/tmp/doc/source/overview.rst:120: WARNING: Include file '/tmp/LICENSE' not found or reading it failed
source/whatsnew/v0.20.0.txt:141: ERROR: Error in "ipython" directive:
invalid option block.
``` needs a white line, pushed a fix to this branch I restarted a couple of times: https://travis-ci.org/pandas-dev/pandas/jobs/209555204

maybe: https://groups.google.com/forum/#!msg/sphinx-dev/MtRf64eGtv4/aOa7FdxkAgAJ

here's a fix (increase stack :>)
```
--- a/docs/users_guide/conf.py
+++ b/docs/users_guide/conf.py
@@ -147,6 +147,8 @@ def parse_flag(env, sig, signode):
 def setup(app):
     from sphinx.util.docfields import Field, TypedField
 
+    increase_python_stack()
+
     # the :ghci-cmd: directive used in ghci.rst
     app.add_object_type('ghci-cmd', 'ghci-cmd',
                         parse_node=parse_ghci_cmd,
@@ -171,3 +173,11 @@ def setup(app):
                             Field('since', label='Introduced in GHC version', names=['since']),
                             Field('static')
                         ])
+
+def increase_python_stack():
+    # Workaround sphinx-build recursion limit overflow:
+    # pickle.dump(doctree, f, pickle.HIGHEST_PROTOCOL)
+    #  RuntimeError: maximum recursion depth exceeded while pickling an object
+    #
+    # Default python allows recursion depth of 1000 calls.
+    sys.setrecursionlimit(10000)
``` https://github.com/sphinx-doc/sphinx/pull/2325/files is a better view on this.