SEC: update supported versions

Anticipate the imminent release of mpl35.

We are now almost 2 years past upstream support for py27 so drop any support
for mpl22.

Author: tacaswell

SECURITY.md

@@ -8,24 +8,23 @@ versions.
 
 | Version | Supported          |
 | ------- | ------------------ |
-| 3.3.x   | :white_check_mark: |
-| 3.2.x   | :white_check_mark: |
-| 3.1.x   | :x:                |
-| 3.0.x   | :x:                |
-| 2.2.x   | :white_check_mark: |
-| < 2.2   | :x:                |
+| 3.5.x   | :white_check_mark: |
+| 3.4.x   | :white_check_mark: |
+| 3.3.x   | :x:                |
+| < 3.3   | :x:                |
+
 
 ## Reporting a Vulnerability
 
-If you have found a security vulnerability, in order to keep it confidential, 
+If you have found a security vulnerability, in order to keep it confidential,
 please do not report an issue on GitHub.
 
-Please email us details of the vulnerability at matplotlib@numfocus.org; 
+Please email us details of the vulnerability at matplotlib@numfocus.org;
 include a description and proof-of-concept that is [short and
 self-contained](http://www.sscce.org/).
 
-You should expect a response within a week of your email. Depending on the 
+You should expect a response within a week of your email. Depending on the
 severity of the issue, this may require some time to draft an immediate bugfix
 release. Less severe issues may be held until the next release.
 
-We do not award bounties for security vulnerabilities. 
+We do not award bounties for security vulnerabilities.