Make MyPluginInfo internal (#11)

In version 1.0.0 `MyPluginInfo`, formerly `PluginInfo`, was an internal class. However due to the v1.0.0 `PluginInfo` not having a project-specific namespace, which came the next update when the internal class was converted to a public class as well, it's properties were not accessible to the plugin's scope. 
With the update seen in v1.1.0 to correctly namespace the class, it can be kept as `internal` and still allow it's variables to be accessed by the defining mod.

## Benefits
When a library mod is referenced by another plugin, the receiving plugin can scope into the library's namespace and also use BepInEx.PluginInfoProps without any confusion about which `MyPluginInfo` is being referenced.

BepInEx.PluginInfoProps/BepInEx.PluginInfoProps.props

@@ -7,7 +7,7 @@
             <GeneratedText><![CDATA[
 namespace $(RootNamespace)
 {
-    public static class MyPluginInfo
+    internal static class MyPluginInfo
     {
         public const string PLUGIN_GUID = "$(BepInExPluginGuid)"%3B
         public const string PLUGIN_NAME = "$(BepInExPluginName)"%3B
@@ -23,4 +23,4 @@ namespace $(RootNamespace)
         </ItemGroup>
         <WriteLinesToFile Lines="$(GeneratedText)" File="$(GeneratedFilePath)" WriteOnlyWhenDifferent="true" Overwrite="true" />
     </Target>
-</Project>
+</Project>