make vector type declaration consistent

Author: johannes-el

en/03_Drawing_a_triangle/00_Setup/02_Validation_layers.adoc

@@ -93,7 +93,7 @@ is part of the c{pp} standard and means "not debug".
 constexpr uint32_t WIDTH = 800;
 constexpr uint32_t HEIGHT = 600;
 
-const std::vector validationLayers = {
+const std::vector<const char*> validationLayers = {
     "VK_LAYER_KHRONOS_validation"
 };
 
@@ -181,9 +181,9 @@ std::vector<const char*> getRequiredExtensions() {
     uint32_t glfwExtensionCount = 0;
     auto glfwExtensions = glfwGetRequiredInstanceExtensions(&glfwExtensionCount);
 
-    std::vector extensions(glfwExtensions, glfwExtensions + glfwExtensionCount);
+    std::vector<const char*> extensions(glfwExtensions, glfwExtensions + glfwExtensionCount);
     if (enableValidationLayers) {
-        extensions.push_back(vk::EXTDebugUtilsExtensionName );
+        extensions.push_back(vk::EXTDebugUtilsExtensionName);
     }
 
     return extensions;