Fix: Bump maxBuffer for Docker solc compilations

[CruzMolina]

Resolves #3140.

[chmanie]

I found that 20MB should suffice (but 100 is probably on the safe side?). I'm not sure what negative implications a high number might have here

[CruzMolina]

@chmanie FWIW, apparently node 10 and lower's default maxBuffer for execSync was set to Infinity 👀: nodejs/node#23027 (comment)

I think 100 should be ok, but would be fine with 20 or 50.

[fainashalts]

👍 LGTM!