fix simple trailing whitespace

fixes #742

https://bugs.ruby-lang.org/issues/7175

@bf4 @jeremy 
it only does on ree, but not on anything else:
```
     Failure/Error: expect(utf8(decode("t=C3=A5=E2=88=82=C6=92t="))).to eq "tå∂ƒt"

       expected: "tå∂ƒt"
            got: "tå∂ƒt="

       (compared using ==)
```