Bump version in README.md

Author: ucbjrl

README.md

@@ -7,7 +7,7 @@ The latest iteration of [Chisel](https://chisel.eecs.berkeley.edu/) is Chisel3,
 which uses Firrtl as an intermediate hardware representation language.
 
 Chisel3 releases are available as jars on Sonatype/Nexus/Maven and as tagged branches on the [releases tab](https://github.com/freechipsproject/chisel3/releases) of this repository.
-The latest release is 3.1.1.
+The latest release is 3.1.2.
 
 Please visit the [Wiki](https://github.com/ucb-bar/chisel3/wiki) for documentation!