[ci skip] Prepare 3.1.8 release
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index 647ea93..371b495 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -5,7 +5,7 @@
 Version 3.1.8
 =============
 
-Release Date: Not Released
+Release Date: Mar 22, 2018
 
 - **Security**