Repair sphinx doc generation

mistake in the log commit neglected to place a space after the `` literal,
which messed up the build by incapacitating the sphinx generator.

Reviewed By: beanz

Differential Revision: https://reviews.llvm.org/D143208

Author: bob80905

clang/docs/ReleaseNotes.rst

@@ -186,7 +186,7 @@ Arm and AArch64 Support in Clang
 
 Floating Point Support in Clang
 -------------------------------
-- Add ``__builtin_elementwise_log``builtin for floating point types only.
+- Add ``__builtin_elementwise_log`` builtin for floating point types only.
 
 Internal API Changes
 --------------------