Update History.markdown

Author: Ch4s3

History.markdown

@@ -9,6 +9,7 @@
  * Memory and Redis backend support ([#84](https://github.com/jekyll/classifier-reborn/pull/84))
 
 ### Minor Enhancements
+ * Validation documentation improvements ([#150](https://github.com/jekyll/classifier-reborn/pull/150))
  * Updated Dokcer image to Ruby 2.4 ([#149](https://github.com/jekyll/classifier-reborn/pull/149))
  * Classifier validation user documenation ([#145](https://github.com/jekyll/classifier-reborn/pull/145))
  * Fixed persistance for BayesMemoryBackend ([#147](https://github.com/jekyll/classifier-reborn/pull/147))