Fix compile failed in stable/beta

src/ffi_util.rs

@@ -18,7 +18,7 @@ use std::ffi::CStr;
 
 pub fn error_message(ptr: *const c_char) -> String {
     let cstr = unsafe { CStr::from_ptr(ptr as *const _) };
-    let s = String::from_utf8_lossy(cstr.to_bytes()).into();
+    let s = String::from_utf8_lossy(cstr.to_bytes()).into_owned();
     unsafe {
         libc::free(ptr as *mut c_void);
     }