(maint) Consolidate case statement in /pson/pure/generator.rb for the Float module.

Prior to this commit, the to_pson method for the Float module contained
unnecessary duplicated code.  This commit removes the duplication by
consolidating the case statements into a single if statement.
Merge pull request #2717 from razalas/fix/master/remove_code_duplication

(maint) Consolidate case statement in /pson/pure/generator.rb for the Fl...