Don't add semi-colons to SQL lines already containing them

[fbertsch]

For a dimension definition:

{
  "name": "field_name",
  "sql": "${TABLE}.field_name ;;"
}

When the lookml is generated, another ;; is appended. I'm seeing two options (there's probably more):

• LookML generation should fail (and the error should be obvious!)
• lkml shouldn't add another ;; during lookml generation