Changed strcpy to memmove to handle memory overlaps

src/app/TCPClient.cpp

@@ -77,6 +77,6 @@ void TCPClient::freeDataBuffer(uint16_t size)
     #endif
   }
   
-  strcpy((char *)_data, (char *)_data + secureSize);
+  memmove(_data, _data + secureSize, _dataSize - secureSize + 1 /*We do not forget to copy the \0 at then end*/);
   _dataSize -= secureSize;
 }