in 1.1.0 they added a couple new features such as privateEncrypt/publicDecrypt functions and publicEncrypt being able to accept a password protected private key (because you can derive a public key from a private key). These where new features so version bump.
1.2.0 added simplified stream construction so instead of being forced to subclass the built ins you could pass transform/flush/read/write/writev options to the constructor, again added feature so minor version.
1.3.0 changed the ordering of the default cipher suites so that more browsers would have perfect forward security by default. While not technically an api addition it's still more then a bug fix as it changes intended behavior so minor version.
1.2.0 added simplified stream construction so instead of being forced to subclass the built ins you could pass transform/flush/read/write/writev options to the constructor, again added feature so minor version.
1.3.0 changed the ordering of the default cipher suites so that more browsers would have perfect forward security by default. While not technically an api addition it's still more then a bug fix as it changes intended behavior so minor version.
All of the releases also a ton of bug fixes.