Updated math lib and import in cargo toml file

math/src/lib.rs

@@ -1,8 +1,6 @@
-mod math {
-    #[allow(dead_code)]
-    pub fn sum(a: i32, b: i32) -> i32 {
-        a + b
-    }
+#[allow(dead_code)]
+pub fn sum(a: i32, b: i32) -> i32 {
+    a + b
 }
 
 #[cfg(test)]
@@ -11,6 +9,6 @@ mod tests {
 
     #[test]
     fn it_works() {
-        assert_eq!(math::sum(10, 10), 20);
+        assert_eq!(sum(10, 10), 20);
     }
 }