docs/network.html: syntax fixups

Fixup for a handful of related syntax errors that I noticed while reading the docs.
- substituted ':' in "var options: {" for a syntactically correct '='.

FYI: same typos not found elsewhere in the source tree:
```
╭─user@box ~/src/vis  ‹cdituri-fixups›
╰─$ grep -riI "var *options *: *{" ./
╭─user@box  ~/src/vis  ‹cdituri-fixups›
╰─$ git grep -iI "var *options *: *{"                                      
```