Update eventmanager.markdown for grammar error and to reflect changes in the sunlight-congress gem

-- Deleted double word "how" on line 368
-- Updated code and instructions regarding the .for_zip method of the sunlight-congress gem to work with the new version of the gem (v. 1.1.0)  by changing .for_zip to .by_zipcode on lines 785, 870, 907, 920, 921, 937, 1063, 1222, 1235, 1251, 1275, 1278, 1281, 1286, 1311, 1370, and 1395
-- Updated code regarding the .all_in_zipcode method of the sunlight-congress gem to work with the new version of the gem (v. 1.1.0)  by changing .all_in_zipcode to .by_zipcode on lines 1234, 1280, and 1369

This is my first open source contribution ever :)