eshost thinks it's an error if JSC prints "x: y"

[rkirsling]

Without exactly one space:

λ eshost -se "'x:y'"
#### ch, jsc, sm, v8, xs
x:y

λ eshost -se "'x:  y'"
#### ch, jsc, sm, v8, xs
x:  y

With exactly one space:

λ eshost -se "'x: y'"
#### ch, sm, v8, xs
x: y

#### jsc

y: undefined

The problem appears to be here, but I don't know what the appropriate solution is: https://github.com/bterlson/eshost/blob/master/lib/agents/jsc.js#L9