chore: fix incorrect version in MANIFEST.MF

[Fiouz]

Fix wrong Implementation-Version and Specification-Version introduced by bdf774e such as (notice the task ':jar' property 'archiveVersion'):

Implementation-Version: task ':jar' property 'archiveVersion'
Import-Package: groovy.lang
Main-Class: picocli.AutoComplete
Multi-Release: true
Require-Capability: osgi.ee;filter:="(&(osgi.ee=JavaSE)(version=1.5))"
Specification-Title: picocli
Specification-Vendor: Remko Popma
Specification-Version: task ':jar' property 'archiveVersion'

(from https://repo1.maven.org/maven2/info/picocli/picocli/4.6.1/picocli-4.6.1.jar / META-INF/MANIFEST.MF)

[codecov]

Codecov Report

Merging #1327 (c003ee6) into master (e5bce48) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1327   +/-   ##
=========================================
  Coverage     93.77%   93.77%           
  Complexity      474      474           
=========================================
  Files             2        2           
  Lines          6957     6957           
  Branches       1867     1867           
=========================================
  Hits           6524     6524           
  Misses          146      146           
  Partials        287      287           

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[remkop]

Merged. Thank you for the pull request!