Port patches from 1.0.0 branch

[hcho3]

• Remove f-string, since it's not supported by Python 3.5 (Remove f-string, since it's not supported by Python 3.5 #5330). This necessitated 1.0.1 patch release.
• Bump version to 1.1.0-SNAPSHOT, to prepare for next release

Also, when I was working on 1.0.1 patch release, I fixed two bugs:

• Enforce only major version in JSON model schema: The schema had 1.0.0 version hard-coded in, so any bump in the version in the codebase would cause schema violation. I revised the schema to only fix the major version. Any major revision of the model schema would bump up the major version.
• Fix a unit test that mistook MINOR ver for PATCH ver: This appears to be a typo in the unit test.

[mli]

Codecov Report

Merging #5336 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5336      +/-   ##
==========================================
- Coverage   83.76%   83.75%   -0.02%     
==========================================
  Files          11       11              
  Lines        2409     2413       +4     
==========================================
+ Hits         2018     2021       +3     
- Misses        391      392       +1     

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