fix: correctly parse sessionId for chrome less 75

[DudaGod]

In the process of implementing #1354, I broke work with the chrome browser version below 75. Response body from chrome@67 looks like this:

{
    sessionId: "session_id",
    status: 0,
    value: {
        browserName: "chrome",
        // ... (without "capabilities" field)
    }
}

In chrome 75 and older looks like this:

{
    value: {
        capabilities: {
            browserName: "chrome",
            // ...
        },
        sessionId: "session_id"
    }
}

It means that sessionId can be located in different places depending on browser version.

[codecov]

Codecov Report

Patch coverage: 61.90% and project coverage change: -0.27 ⚠️

Comparison is base (33d6893) 74.44% compared to head (e18077a) 74.17%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1361      +/-   ##
==========================================
- Coverage   74.44%   74.17%   -0.27%     
==========================================
  Files          12       12              
  Lines        1831     1847      +16     
==========================================
+ Hits         1363     1370       +7     
- Misses        383      391       +8     
- Partials       85       86       +1     

Flag	Coverage Δ
go	74.17% <61.90%> (-0.27%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
selenoid.go	83.12% <61.90%> (-1.34%)	⬇️

... and 1 file with indirect coverage changes

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