Fixed a warning of attempt never being used.

This is due to attempt only being needed when converting sigil members.

src/transmutable.rs

@@ -1,7 +1,8 @@
-use weave::attempt;
-
 use spellbook::components::Array;
 
+#[cfg(feature="convert_sigils")]
+use weave::attempt;
+
 #[cfg(feature="convert_sigils")]
 use sigils::{Zero, Number, Real, Trig};