Fixed the library to use the new Rust 2018 module system.

examples/enums.rs

@@ -7,7 +7,7 @@ c_enum!
 {
    /// Test enum is a simple enum testing the
    /// capabilities of creating a C enum.
-   enum TestEnum : i32
+   enum TestEnum: i32
    {
       /// This is the first item.
       variant One = 1,