terraform: really simple error message fix, direct to master

terraform/interpolate.go

@@ -289,7 +289,7 @@ func (i *Interpolater) valueSimpleVar(
 	return fmt.Errorf(
 		"invalid variable syntax: %q. If this is part of inline `template` parameter\n"+
 			"then you must escape the interpolation with two dollar signs. For\n"+
-			"example: ${a} becomes $${a}." +
+			"example: ${a} becomes $${a}.",
 		n)
 }