vec: compare length and capacity in the same order as in Vec::push

src/vec/vec-final.md

@@ -127,7 +127,7 @@ impl<T> Vec<T> {
 
     pub fn insert(&mut self, index: usize, elem: T) {
         assert!(index <= self.len, "index out of bounds");
-        if self.cap() == self.len {
+        if self.len == self.cap() {
             self.buf.grow();
         }
 

src/vec/vec-insert-remove.md

@@ -18,7 +18,7 @@ pub fn insert(&mut self, index: usize, elem: T) {
     // Note: `<=` because it's valid to insert after everything
     // which would be equivalent to push.
     assert!(index <= self.len, "index out of bounds");
-    if self.cap == self.len { self.grow(); }
+    if self.len == self.cap { self.grow(); }
 
     unsafe {
         // ptr::copy(src, dest, len): "copy from src to dest len elems"