Fix type error with ? in existing code.

Author: nrc

src/librustc/ty/relate.rs

@@ -151,13 +151,13 @@ pub fn relate_substs<'a, 'gcx, 'tcx, R>(relation: &mut R,
         let b_ty = &b_subst.types[i];
         let variance = variances.map_or(ty::Invariant, |v| v.types[i]);
         relation.relate_with_variance(variance, a_ty, b_ty)
-    }).collect()?;
+    }).collect::<Result<_, _>>()?;
 
     let regions = a_subst.regions.iter().enumerate().map(|(i, a_r)| {
         let b_r = &b_subst.regions[i];
         let variance = variances.map_or(ty::Invariant, |v| v.regions[i]);
         relation.relate_with_variance(variance, a_r, b_r)
-    }).collect()?;
+    }).collect::<Result<_, _>>()?;
 
     Ok(Substs::new(tcx, types, regions))
 }