Update Exercises Directory Names to Reflect Order

exercises/01_variables/variables5.rs

@@ -0,0 +1,13 @@
+// variables5.rs
+//
+// Execute `rustlings hint variables5` or use the `hint` watch subcommand for a
+// hint.
+
+// I AM NOT DONE
+
+fn main() {
+    let number = "T-H-R-E-E"; // don't change this line
+    println!("Spell a Number : {}", number);
+    number = 3; // don't rename this variable
+    println!("Number plus two is : {}", number + 2);
+}