Merge recent update from ch7 && cargo clippy

easy-fs/src/bitmap.rs

@@ -17,7 +17,7 @@ pub struct Bitmap {
 /// Return (block_pos, bits64_pos, inner_pos)
 fn decomposition(mut bit: usize) -> (usize, usize, usize) {
     let block_pos = bit / BLOCK_BITS;
-    bit = bit % BLOCK_BITS;
+    bit %= BLOCK_BITS;
     (block_pos, bit / 64, bit % 64)
 }
 
@@ -70,4 +70,4 @@ impl Bitmap {
     pub fn maximum(&self) -> usize {
         self.blocks * BLOCK_BITS
     }
-}
+}