Bug with map returned from lamba single arg, missing outer braces that are needed

[ldemailly]

Started as a more complex one in discord bot but reduced to :

$ ()=>{{"a":1,"b":2}}
()=>{"a":1,"b":2}

which doesn't work when reloaded:

parser error: no prefix parse function for `,` found:
()=>{"a":1,"b":2}
          ^

• test failing
• fix

[ccoVeille]

LGTM 👍