DOC: fixing hyperlink in documentation (#533)

Author: glemaitre

doc/conf.py

@@ -38,7 +38,6 @@
  'sphinx.ext.doctest',
  'sphinx.ext.intersphinx',
  'sphinx.ext.linkcode',
- 'sphinx.ext.viewcode',
  'numpydoc',
  'sphinx_issues',
  'sphinx_gallery.gen_gallery',