set script path in Windows launch script (#777)

docs/release-notes.md

@@ -8,6 +8,9 @@
 -->
 
 ## Upcoming release
+* For players:
+  * Fixed error when running the Windows installer as administrator (thanks to LostLogic!).
+
 * For mod authors:
   * Added validation for the manifest `Dependencies` field.
   * Fixed validation for mods with version `0.0.0`.

src/SMAPI.Installer/assets/windows-install.bat

@@ -4,5 +4,6 @@ if not errorlevel 1 (
    echo Oops! It looks like you're running the installer from inside a zip file. Make sure you unzip the download first.
    pause
 ) else (
+   cd "%~dp0"
    start /WAIT /B ./internal/windows-install.exe
 )