Fix RTM_CONNECTION_OPENED event name

[marclemagne]

Summary

Fixes a typo in README for RTM_CONNECTION_OPEN to be RTM_CONNECTION_OPENED.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #446 into master will increase coverage by 0.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #446      +/-   ##
==========================================
+ Coverage    89.1%   89.25%   +0.14%     
==========================================
  Files          44       44              
  Lines        1258     1275      +17     
  Branches      190      194       +4     
==========================================
+ Hits         1121     1138      +17     
  Misses        137      137

Impacted Files	Coverage Δ
lib/clients/transports/request.js	90.9% <0%> (+4.06%)	⬆️

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[aoberoi]

good catch!!