Change 'nonnegative' to 'non-negative' for consistency

[fingolfin]

No description provided.

[codecov]

Codecov Report

Merging #942 (6858cd2) into master (5471f12) will not change coverage.
The diff coverage is 66.66%.

@@           Coverage Diff           @@
##           master     #942   +/-   ##
=======================================
  Coverage   75.78%   75.78%           
=======================================
  Files          51       51           
  Lines        4162     4162           
=======================================
  Hits         3154     3154           
  Misses       1008     1008           

Files Changed	Coverage
pkg/JuliaExperimental/gap/finvar.gi	0.00%
pkg/JuliaInterface/gap/adapter.gi	100.00%

[ThomasBreuer]

O.k.
Concerning consistency, I think "nonnegative" occured more often in GAP.jl than "non-negative". Oscar.jl has a clear majority for "non-negative", and gap-system has a small majority for "non-negative". So let us switch to "non-negative".