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/hash.rs

@@ -15,10 +15,10 @@ pub struct Hasher {
 }
 
 impl Hasher {
-    pub fn hash(&mut self, val: &[u8]) -> () {
+    pub fn hash(&mut self, val: &[u8]) {
         self.hasher.input(val);
     }
-    pub fn hashv(&mut self, vals: &[&[u8]]) -> () {
+    pub fn hashv(&mut self, vals: &[&[u8]]) {
         for val in vals {
             self.hash(val);
         }

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(

sdk/src/transaction.rs

@@ -293,7 +293,8 @@ mod tests {
             14, 229, 239, 119, 93, 5, 218, 161, 35, 3, 33, 0, 36, 100, 158, 252, 33, 161, 97, 185,
             62, 89, 99, 195, 250, 249, 187, 189, 171, 118, 241, 90, 248, 14, 68, 219, 231, 62, 157,
             5, 142, 27, 210, 117,
-        ])).expect("fu");
+        ]))
+        .unwrap();
         let to = Pubkey::new(&[
             1, 1, 1, 4, 5, 6, 7, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 8, 7, 6, 5, 4,
             1, 1, 1,