Increase version in userguide to 3.1.4-dev

The version number was not increased after the 3.1.3 release.
diff --git a/user_guide_src/source/conf.py b/user_guide_src/source/conf.py
index 5c447b7..2df5f9e 100644
--- a/user_guide_src/source/conf.py
+++ b/user_guide_src/source/conf.py
@@ -48,9 +48,9 @@
 # built documents.
 #
 # The short X.Y version.
-version = '3.1.3-dev'
+version = '3.1.4-dev'
 # The full version, including alpha/beta/rc tags.
-release = '3.1.3-dev'
+release = '3.1.4-dev'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.