Update changelog.

Author: Semigradsky

CHANGELOG.md

@@ -1,3 +1,7 @@
+# 2.1.3 - 2017-11-27
+
+- Fixed: Incorrect reduction for a specific case (e.g. `calc(1em + (1em - 5px))`) ([#43](https://github.com/MoOx/reduce-css-calc/pull/43) - @Justineo)
+
 # 2.1.2 - 2017-11-26
 
 - Fixed: Incorrect reduction of division with custom property (e.g. `calc(var(--foo) / 2)`) ([#41](https://github.com/MoOx/reduce-css-calc/issues/41) - @Semigradsky)