DOC: Fix typo in picocli user manual

[sakata1222]

I found a typo in the "Guice Example".

• The method variable name of GuiceFactory#create is aClass.
• I think the 1st argument of new CommandLine should have annotations of picocli, so we should specify a implemented class (i.e. InjectionDemo.class) not Runnable.class
• If we specify the implemented class, bind definition for Runnable.class might be unnecessary.

[codecov-commenter]

Codecov Report

Merging #1116 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1116   +/-   ##
=========================================
  Coverage     94.36%   94.36%           
  Complexity      448      448           
=========================================
  Files             2        2           
  Lines          6633     6633           
  Branches       1782     1782           
=========================================
  Hits           6259     6259           
  Misses           99       99           
  Partials        275      275           

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[sakata1222]

I found the other mistakes, I will update and reopen this pull request.

[remkop]

Merged into master.
Thank you for the contribution!