Merge branch 'release-v2.2.0'

CHANGELOG.md

 # Changelog
 
-## 2.2.0 (unreleased)
+## 2.2.0 (2019-03-14)
 
 ### New features:
  * `ERC20Snapshot`: create snapshots on demand of the token balances and total supply, to later retrieve and e.g. calculate dividends at a past time. ([#1617](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1617))

ethpm.json

 {
   "package_name": "zeppelin",
-  "version": "2.1.3",
+  "version": "2.2.0",
   "description": "Secure Smart Contract library for Solidity",
   "authors": [
     "OpenZeppelin Community <maintainers@openzeppelin.org>"

package-lock.json

 {
   "name": "openzeppelin-solidity",
-  "version": "2.1.3",
+  "version": "2.2.0",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {

package.json

 {
   "name": "openzeppelin-solidity",
-  "version": "2.1.3",
+  "version": "2.2.0",
   "description": "Secure Smart Contract library for Solidity",
   "files": [
     "build",