Error message while starting rails server

I am getting the below errors whenever i try to start my rails server
("rails s") or install a new gem. Can ne1 tell me how to get rid of
them?

Invalid gemspec in [/var/lib/gems/1.8/specifications/
tilt-1.3.3.gemspec]: invalid date format in specification: "2011-08-25
00:00:00.000000000Z"
Invalid gemspec in [/var/lib/gems/1.8/specifications/
hashie-1.2.0.gemspec]: invalid date format in specification:
"2011-10-15 00:00:00.000000000Z"
Invalid gemspec in [/var/lib/gems/1.8/specifications/
oauth2-0.5.2.gemspec]: invalid date format in specification:
"2012-01-04 00:00:00.000000000Z"
Invalid gemspec in [/var/lib/gems/1.8/specifications/
faraday-0.7.5.gemspec]: invalid date format in specification:
"2011-10-04 00:00:00.000000000Z"
Invalid gemspec in [/var/lib/gems/1.8/specifications/
instagram-0.8.gemspec]: invalid date format in specification:
"2011-08-15 00:00:00.000000000Z"

http://blog.rubygems.org/2011/08/31/shaving-the-yaml-yak.html

TL;DR:

gem update --system
gem pristine --all

Then do "gem install <name>" for the gems still showing "Invalid
gemspec" error

PS: This was already answered here and all over the internet
(including stackoverflow). Search is your friend.