Fix warnings: single tuples

ethcore/src/tx_filter.rs

@@ -52,7 +52,7 @@ pub struct TransactionFilter {
     contract_address: Address,
     transition_block: BlockNumber,
     permission_cache: Mutex<LruCache<(H256, Address), u32>>,
-    contract_version_cache: Mutex<LruCache<(H256), Option<U256>>>,
+    contract_version_cache: Mutex<LruCache<H256, Option<U256>>>,
 }
 
 impl TransactionFilter {

ethcore/sync/src/light_sync/sync_round.rs

@@ -251,7 +251,7 @@ impl Fetcher {
                 }
 
                 // state transition not triggered until drain is finished.
-                (SyncRound::Fetch(self))
+                SyncRound::Fetch(self)
             }
         }
     }

util/EIP-712/src/encode.rs

@@ -45,7 +45,7 @@ fn check_hex(string: &str) -> Result<()> {
 fn build_dependencies<'a>(
     message_type: &'a str,
     message_types: &'a MessageTypes,
-) -> Option<(HashSet<&'a str>)> {
+) -> Option<HashSet<&'a str>> {
     if message_types.get(message_type).is_none() {
         return None;
     }