Fix and format basic_ostream::sentry syntax

Author: Rageking8

docs/standard-library/basic-ostream-class.md

@@ -450,12 +450,13 @@ int main()
 The nested class describes an object whose declaration structures the formatted output functions and the unformatted output functions.
 
 ```cpp
-class sentry {
-   public:
-   explicit sentry(basic_ostream\<Elem, Tr>& _Ostr);
-   operator bool() const;
-   ~sentry();
-   };
+class sentry
+{
+public:
+    explicit sentry(basic_ostream<Elem, Tr>& _Ostr);
+    operator bool() const;
+    ~sentry();
+};
 ```
 
 ### Remarks