docs: update examples

[snitin315]

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

Motivation / Use-Case

Update examples to use --open-target <url>, --open-target is not boolean anymore after #3496.

Breaking Changes

None

Additional Info

No

[codecov]

Codecov Report

Merging #3505 (190b4ba) into master (0020f3e) will decrease coverage by 0.01%.
The diff coverage is 95.05%.

@@            Coverage Diff             @@
##           master    #3505      +/-   ##
==========================================
- Coverage   94.35%   94.34%   -0.02%     
==========================================
  Files          26       20       -6     
  Lines        1276     1291      +15     
  Branches      402      417      +15     
==========================================
+ Hits         1204     1218      +14     
- Misses         66       68       +2     
+ Partials        6        5       -1     

Impacted Files	Coverage Δ
bin/cli-flags.js	100.00% <ø> (ø)
lib/Server.js	93.68% <90.60%> (-0.63%)	⬇️
client-src/index.js	88.23% <100.00%> (+5.04%)	⬆️
client-src/utils/createSocketURL.js	100.00% <100.00%> (+3.57%)	⬆️
client-src/utils/parseURL.js	90.00% <100.00%> (-10.00%)	⬇️
client-src/utils/reloadApp.js	82.60% <100.00%> (-4.35%)	⬇️
lib/servers/SockJSServer.js	95.23% <100.00%> (+4.54%)	⬆️
lib/servers/WebsocketServer.js	89.47% <100.00%> (-7.90%)	⬇️
lib/utils/DevServerPlugin.js	98.61% <100.00%> (+1.01%)	⬆️
lib/utils/normalizeOptions.js	97.17% <100.00%> (+0.62%)	⬆️
... and 5 more

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[alexander-akait]

I think we should change --open-target on --open as before, it is most usage and simply

[snitin315]

Yes, will do.