Upgrade to Rust 1.31.0 (#2052)

* Upgrade to Rust 1.31.0
* Upgrade nightly
* Fix all clippy warnings
* Revert relaxed version check and update

sdk/src/system_transaction.rs

@@ -107,7 +107,8 @@ impl SystemTransaction for Transaction {
             .map(|(i, (_, amount))| {
                 let spend = SystemInstruction::Move { tokens: *amount };
                 Instruction::new(0, &spend, vec![0, i as u8 + 1])
-            }).collect();
+            })
+            .collect();
         let to_keys: Vec<_> = moves.iter().map(|(to_key, _)| *to_key).collect();
 
         Transaction::new_with_instructions(