fix/test: link against cudart for cuda allocation

Author: drahnr

cudnn/tests/cudnn_specs.rs

@@ -5,6 +5,9 @@ extern crate libc;
 extern crate rcudnn_sys as ffi;
 use ffi::*;
 
+#[cfg(test)]
+#[link(name = "cudart")]
+
 #[cfg(test)]
 mod cudnn_spec {