Local version identifier is not repected (starting from plus sign)

[tyger]

It seems that bump2version doesn't respect Local Version Identifier when specified in current version config or cli param.

Local version according to PEP 440 is part after Public Version Identifier and starts with +, for example: 1.2.3+ubuntu.1. In this case bump2version only uses public version part and search for 1.2.3 in files, regecting +ubuntu.1 part.