chore: Correct test command in tests1.rs comment (rust-lang#267)

chore: Correct test command in tests1.rs comment

Author: fmoko

exercises/tests/tests1.rs

@@ -1,7 +1,7 @@
 // tests1.rs
 // Tests are important to ensure that your code does what you think it should do.
 // Tests can be run on this file with the following command:
-// rustlings run exercises/tests/tests1.rs
+// rustlings run tests1
 
 // This test has a problem with it -- make the test compile! Make the test
 // pass! Make the test fail! Execute `rustlings hint tests1` for hints :)