Update note about test value sources

tests/pass/float.rs

@@ -468,7 +468,7 @@ macro_rules! test_ftof {
     }};
 }
 
-/// Many of these test values are taken from
+/// Many of these test patterns were adapted from the values in
 /// https://github.com/WebAssembly/testsuite/blob/master/conversions.wast.
 fn casts() {
     /* int <-> float generic tests */