use custom material for skybox

Assets/Materials/Skybox.mat

@@ -0,0 +1,30 @@
+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!21 &2100000
+Material:
+  serializedVersion: 6
+  m_ObjectHideFlags: 0
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_Name: Skybox
+  m_Shader: {fileID: 106, guid: 0000000000000000f000000000000000, type: 0}
+  m_ShaderKeywords: _MAPPING_LATITUDE_LONGITUDE_LAYOUT _SUNDISK_HIGH_QUALITY
+  m_LightmapFlags: 4
+  m_EnableInstancingVariants: 0
+  m_DoubleSidedGI: 0
+  m_CustomRenderQueue: -1
+  stringTagMap: {}
+  disabledShaderPasses: []
+  m_SavedProperties:
+    serializedVersion: 3
+    m_TexEnvs: []
+    m_Floats:
+    - _AtmosphereThickness: 1
+    - _Exposure: 0.979043
+    - _SunDisk: 2
+    - _SunSize: 0.04
+    - _SunSizeConvergence: 5
+    m_Colors:
+    - _GroundColor: {r: 0.369, g: 0.349, b: 0.341, a: 1}
+    - _SkyTint: {r: 0.5, g: 0.5, b: 0.5, a: 1}

Assets/Materials/Skybox.mat.meta

@@ -0,0 +1,8 @@
+fileFormatVersion: 2
+guid: bb40896b23508b74bbe272607c7ab295
+NativeFormatImporter:
+  externalObjects: {}
+  mainObjectFileID: 2100000
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Scenes/Main.unity

@@ -26,7 +26,7 @@ RenderSettings:
   m_AmbientIntensity: 1
   m_AmbientMode: 3
   m_SubtractiveShadowColor: {r: 0.42, g: 0.478, b: 0.627, a: 1}
-  m_SkyboxMaterial: {fileID: 10304, guid: 0000000000000000f000000000000000, type: 0}
+  m_SkyboxMaterial: {fileID: 2100000, guid: bb40896b23508b74bbe272607c7ab295, type: 2}
   m_HaloStrength: 0.5
   m_FlareStrength: 1
   m_FlareFadeSpeed: 3