Update Warning in abs()

Updated Warning acc to arduino/Arduino#2602

Author: Akshay Sharma

Language/Functions/Math/abs.adoc

@@ -48,8 +48,8 @@ Because of the way the abs() function is implemented, avoid using other function
 ----
 abs(a++);   // avoid this - yields incorrect results
 
-a++;          // use this instead -
-abs(a);       // keep other math outside the function
+abs(a);         // use this instead -
+a++;        // keep other math outside the function
 ----
 [%hardbreaks]