New string interpolation breaks parser

[stroan]

Hitting the following error on master:

$ echo {} | ./jq '{foo: "s"}'

error: syntax error, unexpected QQSTRING_START
{foo: "s"}
      ^
1 compile error

Used git bisect to narrow it down to this commit: afec254

[stedolan]

Silly mistake. The syntax for expressions is slightly different after a : in a dictionary, in particular comma means something different. Moving String out of Exp into Term makes it available in that context as well.