Use RTD theme

diff --git a/doc/conf.py b/doc/conf.py
index d59973a..c8bdc94 100644
--- a/doc/conf.py
+++ b/doc/conf.py

@@ -43,7 +43,7 @@
 
 # General information about the project.
 project = u'sphinxcontrib-doxylink'
-copyright = u'2017, Matt Williams'
+copyright = u'2022, Matt Williams'
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
@@ -93,7 +93,7 @@
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-html_theme = 'sphinxdoc'
+html_theme = "sphinx_rtd_theme"
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the