Update cmake to 3.14

[jmklix]

Issue #, if available:

Description of changes:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.11%. Comparing base (ae7b067) to head (6bc9513).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1102   +/-   ##
=======================================
  Coverage   83.11%   83.11%           
=======================================
  Files          56       56           
  Lines        5764     5764           
=======================================
  Hits         4791     4791           
  Misses        973      973           

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[graebm]

We updated to CMake 3.9 here: https://github.com/awslabs/aws-c-common/pull/1159 That's the highest we could go, due to still needing to build on RHEL5