Merge pull request #22 from mykmelez/update-minimum-rust-version

fix build bustage on obsolete and nightly Rust

.travis.yml

@@ -9,7 +9,7 @@ os:
   - osx
 
 rust:
-- 1.20.0
+- 1.30.0
 - stable
 - nightly
 

src/transaction.rs

@@ -448,7 +448,7 @@ mod test {
         {
             let mut cur = txn.open_ro_cursor(db).unwrap();
             let iter = cur.iter_dup_of(b"key1");
-            let vals = iter.map(|(_,x)| x).collect::<Vec<_>>();
+            let vals = iter.map(|x| x.unwrap()).map(|(_,x)| x).collect::<Vec<_>>();
             assert_eq!(vals, vec![b"val1", b"val2", b"val3"]);
 
         }
@@ -463,7 +463,7 @@ mod test {
         {
             let mut cur = txn.open_ro_cursor(db).unwrap();
             let iter = cur.iter_dup_of(b"key1");
-            let vals = iter.map(|(_,x)| x).collect::<Vec<_>>();
+            let vals = iter.map(|x| x.unwrap()).map(|(_,x)| x).collect::<Vec<_>>();
             assert_eq!(vals, vec![b"val1", b"val3"]);
 
             let iter = cur.iter_dup_of(b"key2");