Fix gcc warning (by default an error) when using raygui from C++ (#183)

In C, string literals have the type char*, but you cannot write to them. In C++, they have the type const char*

src/raygui.h

@@ -3147,7 +3147,7 @@ int GuiTextInputBox(Rectangle bounds, const char *title, const char *message, co
     if (secretViewActive != NULL)
     {
         if (GuiTextBox(RAYGUI_CLITERAL(Rectangle){ textBoxBounds.x, textBoxBounds.y, textBoxBounds.width - 4 - RAYGUI_TEXTINPUTBOX_HEIGHT, textBoxBounds.height }, 
-            ((*secretViewActive == 1) || textEditMode)? text : "****************", textMaxSize, textEditMode)) textEditMode = !textEditMode;
+            ((*secretViewActive == 1) || textEditMode)? text : (char *) "****************", textMaxSize, textEditMode)) textEditMode = !textEditMode;
 
         *secretViewActive = GuiToggle(RAYGUI_CLITERAL(Rectangle){ textBoxBounds.x + textBoxBounds.width - RAYGUI_TEXTINPUTBOX_HEIGHT, textBoxBounds.y, RAYGUI_TEXTINPUTBOX_HEIGHT, RAYGUI_TEXTINPUTBOX_HEIGHT }, (*secretViewActive == 1)? "#44#" : "#45#", *secretViewActive);
     }