std: Bump time margin in std::time tests

I believe that because Windows' unit of resolution is 100ns that this unit of
time will ensure that the assertions will hold true as it's representable in the
native format.

cc rust-lang#29970

Author: alexcrichton

src/libstd/time/mod.rs

@@ -235,7 +235,7 @@ mod tests {
             let (a, b) = ($a, $b);
             if a != b {
                 let (a, b) = if a > b {(a, b)} else {(b, a)};
-                assert!(a - Duration::new(0, 1) <= b);
+                assert!(a - Duration::new(0, 100) <= b);
             }
         })
     }