Fix url error in API page

[saneery]

#2585

Motivation

There is a bug with the url on calling of API methods. JS code runs a query just to https://blockscout.com/api it should be with a full path like this https://blockscout.com/eth/mainnet/api

Checklist for your PR

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so if necessary
• If I added/changed/removed ENV var, I should update the list of env vars in https://github.com/poanetwork/blockscout/blob/master/docs/env-variables.md to reflect changes in the table here https://poanetwork.github.io/blockscout/#/env-variables?id=blockscout-env-variables. I've set master in the Version column.
• If I add new indices into DB, I checked, that they don't redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build ecc9718a-b232-41f3-b684-ca6246f3fdff

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 79.086%

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Totals
Change from base Build 91cc4c90-1174-4126-86cb-ce14979529dd:	0.06%
Covered Lines:	5207
Relevant Lines:	6584

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💛 - Coveralls

[vbaranov]

curl -X POST --data '{"id":0,"jsonrpc":"2.0","method": "eth_getBalance", "params": []}'

Copy button copies it without double-quotes in params

[vbaranov]

@saneery

[vbaranov]

@saneery

1. protocol should be indicated

2. An example is not full - an endpoint is empty. It is a bad UX for users. They should be able to copy/paste the command to the terminal.

[vbaranov]

@saneery