(CI) fix rtd warning static directory

Why: Something on read the docs end

How: Remove _static from conf.py

See: readthedocs/readthedocs.org#1776

Tags: continuous integration documentation

Author: 8563a236e65cede7b14220e65c70ad5718144a3

docs/source/conf.py

@@ -55,7 +55,7 @@
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = []
 
 # -- Enable Intersphinx ------------------------------------------------------
 intersphinx_mapping = {'http://docs.python.org/': None, }