Added Zapier Tutorials, Minor Edits, Fixed Caching Error

[eschallock]

• /Integrate/Tutorials/Zapier/ - we added several tutorials for SendGrid/Zapier integration:
  • Sending New Emails via SendGrid For New Gravity Form Submissions
  • Send Emails Through SendGrid For New Caught Webhook Data
  • Sending SendGrid Emails For New PostgreSQL Custom Query Row Matches
  • Sending SendGrid Emails From New Google Sheets Rows
  • Sending Emails From SendGrid to Tagged Infusionsoft Contacts
  • Sending SendGrid Email When New Firebase Child Records Are Added
• /User_Guide/Marketing_Campaigns/index.html - updated the video on Marketing Campaigns index page
• /API_Reference/Web_API/Customer_Subuser_API/multi_cred.html - fixed typo
• /Glossary/ - edited Automated Email related entries to include "automation" for better search results:
  • automated_email.html
  • triggered_email.html
  • triggered_actions.html
  • triggering_events.html
• Edited Gemfile and Gemfile.lock to resolve error with changes in Develop not being displayed on sendgrid.com/docs after merging to Master