Content-Disposition, be permissive sans whitespace

As noted [here](https://github.com/exercism/pharo/issues/96#issuecomment-421095511), while writing a GUI client for Pharo I discovered the server is quite picky in requiring a whitespace following "**form-data;**" in the "Content-Disposition:" field.

After a couple of hours hunting various RFCs I couldn't find that requirement anywhere. While Pharo will be able to work around it, but this situation may impede others trying making a custom client, so consider being more permissive in the line structure.

Here is the pertinent line extracted from a Wireshark captures...

CLI generated the following which works fine...
```Content-Disposition: form-data; name="files[]"; filename="myfile.txt" ```

Pharo generated the following and gets "500 INTERNAL SERVER ERROR"...
```Content-Disposition: form-data;name="files[]";filename="myfile.txt" ```

A diff of the full requests plus library code change is here... https://www.diffchecker.com/ETIfCUzx
Note its actually only the first space-after-semicolon that it the problem.