Upgrade hcl to v2

Signed-off-by: Patrick Van Stee <patrick@vanstee.me>

vendor/github.com/zclconf/go-cty/cty/null.go

@@ -0,0 +1,14 @@
+package cty
+
+// NullVal returns a null value of the given type. A null can be created of any
+// type, but operations on such values will always panic. Calling applications
+// are encouraged to use nulls only sparingly, particularly when user-provided
+// expressions are to be evaluated, since the precence of nulls creates a
+// much higher chance of evaluation errors that can't be caught by a type
+// checker.
+func NullVal(t Type) Value {
+	return Value{
+		ty: t,
+		v:  nil,
+	}
+}