Update FDL CHANGELOG for M46. (#2646)

* Update FDL CHANGELOG for M46.

* Add space.

Firebase/DynamicLinks/CHANGELOG.md

@@ -1,3 +1,6 @@
+# v3.4.3
+- Fixed an issue where matchesshortlinkformat was returning true for certain FDL long links.
+
 # v3.4.2
 - Fixes an issue with certain analytics attribution parameters not being recorded on an app install. (#2462)