Fix bug with convert

Author: jhpratt

tests/convert.rs

@@ -0,0 +1,7 @@
+use rstest::rstest;
+use time::convert::*;
+
+#[rstest]
+fn issue_749() {
+    assert_eq!(Nanosecond::per(Second), 1_000_000_000u32);
+}

tests/main.rs

@@ -112,6 +112,7 @@ require_all_features! {
         }}
     }
 
+    mod convert;
     mod date;
     mod derives;
     mod duration;

time-core/src/convert.rs

@@ -99,7 +99,7 @@ macro_rules! impl_per {
                 const VALUE: $float_output = $float_value;
             })+
 
-            impl DefaultOutput<$larger> for $t {
+            impl DefaultOutput<$t> for $larger {
                 type Output = $default_output;
             }
         )+