add File and Program to builder keys

lib/6to5/types/builder-keys.json

@@ -6,6 +6,7 @@
   "CallExpression":          ["callee", "arguments"],
   "ConditionalExpression":   ["test", "consequent", "alternate"],
   "ExpressionStatement":     ["expression"],
+  "File":                    ["program", "comments", "tokens"],
   "FunctionExpression":      ["id", "params", "body"],
   "Identifier":              ["name"],
   "IfStatement":             ["test", "consequent", "alternate"],
@@ -13,6 +14,7 @@
   "MemberExpression":        ["object", "property", "computed"],
   "ObjectExpression":        ["properties"],
   "ParenthesizedExpression": ["expression"],
+  "Program":                 ["body"],
   "Property":                ["kind", "key", "value", "computed"],
   "ReturnStatement":         ["argument"],
   "SequenceExpression":      ["expressions"],