update(rez-pip): update the README file for vendor libraries

src/rez/vendor/README.md

@@ -18,7 +18,7 @@ Note that the latest versions column is just to give us an idea of how far back
 | argparse                    | 1.2.1                      | Python standard library since 2.7,>=3.2 | We should simply drop support for python <2.6. Note: Can be done now, 2.6 already officially dropped.                                                                                                                                                                                         |
 | atomicwrites                | 1.2.1 (Aug 30, 2018)       | 1.3.0 (Feb 1, 2019)                     |                                                                                                                                                                                                                                       |
 | colorama                    | 0.3.1 (Apr 19, 2014)       | 0.4.1 (Nov 25, 2018)                    | The newest version probably support Windows :)                                                                                                                                                                                        |
-| distlib                     | 0.2.4.dev0 (~Sep 30, 2016) | 0.2.8 (Oct 1, 2018)                     | Why are we living on a development version?                                                                                                                                                                                           |
+| distlib                     | 0.2.9.post0 (May 14, 2019) | 0.3.0 (No official release yet)         | Updated (June 2019) to enable wheel distribution based installations                                                                                                                                                                                           |
 | enum                        | ?                          | ?                                       | By looking at the code, it's probably enum34. If so, the latest version is 1.1.6 (May 15, 2016)                                                                                                                                       |
 | lockfile                    | 0.9.1 (Sep 19, 2010)       | 0.12.2 (Nov 25, 2015)                   |                                                                                                                                                                                                                                       |
 | memcache (python-memcached) | 1.53 (Jun 7, 2013)         | 1.59 (Dec 15, 2017)                     | We could try to move to a more maintained package like pymemcache from pinterest. NOTE: A port to redis may be a better option, people are more familiar with it and it already has a good python client that supports conn pooling.                                                                                                                                                     |