Fix for Java 5 and 6 JVMs

[sjsajj]

Fixing the dependency on Java 7 by removing the java.util.Objects.requireNonNull calls.
The project will now be able to run on Java 5 JVMs again.

[codecov-io]

Codecov Report

Merging #214 into master will not change coverage.
The diff coverage is 50%.

@@            Coverage Diff            @@
##             master     #214   +/-   ##
=========================================
  Coverage     86.62%   86.62%           
  Complexity      148      148           
=========================================
  Files             4        4           
  Lines          1839     1839           
  Branches        460      460           
=========================================
  Hits           1593     1593           
  Misses          126      126           
  Partials        120      120

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/picocli/CommandLine.java	89.07% <50%> (ø)	87 <0> (ø)	⬇️

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[remkop]

Good catch, thank you!

[remkop]

The codecov plugin prevents me from merging this on my phone. (Unsure why, looks like a codecov bug.)
I’ll merge this when I get back to my pc tonight.

[remkop]

This has been merged into master, and a new release (v2.0.1) is now available from Maven Central and JCentral.

Thanks again for the PR!