fix MSSQL placeholders

Signed-off-by: Billy Yuan <billy112487983@gmail.com>

Author: BillyYccc

vertx-mssql-client/src/main/java/io/vertx/mssqlclient/impl/MSSQLConnectionImpl.java

@@ -30,7 +30,7 @@ public MSSQLConnectionImpl(MSSQLConnectionFactory factory, ContextInternal conte
 
   @Override
   public int appendQueryPlaceholder(StringBuilder queryBuilder, int index, int current) {
-    queryBuilder.append('@').append(1 + index);
+    queryBuilder.append('@').append('P').append(1 + index);
     return index;
   }
 

vertx-mssql-client/src/main/java/io/vertx/mssqlclient/impl/MSSQLPoolImpl.java

@@ -42,7 +42,7 @@ private MSSQLPoolImpl(ContextInternal context, boolean closeVertx, MSSQLConnecti
 
   @Override
   public int appendQueryPlaceholder(StringBuilder queryBuilder, int index, int current) {
-    queryBuilder.append('@').append(1 + index);
+    queryBuilder.append('@').append('P').append(1 + index);
     return index;
   }