Update docs version and clear release notes after 8.0.0 version bump

llvm-svn: 338558
diff --git a/lld/docs/conf.py b/lld/docs/conf.py
index 3598fbf..62404b2 100644
--- a/lld/docs/conf.py
+++ b/lld/docs/conf.py
@@ -48,9 +48,9 @@
 # built documents.
 #
 # The short version.
-version = '7'
+version = '8'
 # The full version, including alpha/beta/rc tags.
-release = '7'
+release = '8'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.