更新 0142.环形链表II go版本

1、原先的Go版本代码显示错乱，一部分代码未显示
2、去掉多余判断，让代码更简洁

problems/0142.环形链表II.md

@@ -234,25 +234,19 @@ class Solution:
 ```
 
 Go：
-```func detectCycle(head *ListNode) *ListNode {
-    if head ==nil{
-        return head 
-    }
-    slow:=head
-    fast:=head.Next
-
-    for fast!=nil&&fast.Next!=nil{
-        if fast==slow{
-            slow=head
-            fast=fast.Next
-            for fast!=slow {
-                fast=fast.Next
-                slow=slow.Next
+```go
+func detectCycle(head *ListNode) *ListNode {
+    slow, fast := head, head
+    for fast != nil && fast.Next != nil {
+        slow = slow.Next
+        fast = fast.Next.Next
+        if slow == fast {
+            for slow != head {
+                slow = slow.Next
+                head = head.Next
             }
-            return slow
+            return head
         }
-        fast=fast.Next.Next
-        slow=slow.Next
     }
     return nil
 }