Added changes to the changelog.

todonotes.dtx

@@ -196,6 +196,10 @@
 %             suggested by ErikBoesen.}
 % \changes{1.0.7}{2018/07/09}{Changed the warning about marginparwidth to a
 %             proper warning message.}
+% \changes{1.0.8}{2018/09/08}{Improved spacing behaviour so it mimics the index macro,
+%             patch by Frank Mittelbach.
+%             Center graphics vertically in missingfigure, patch by Philipp Allgeuer.
+%             Added new option tickmarkheight as suggested by Richard Niland.}
 % \GetFileInfo{todonotes.dtx}
 %
 % \DoNotIndex{\newcommand,\newenvironment}