Fixing MahApps NuSpec (#1677)

Author: Keboo

MaterialDesignThemes.MahApps.nuspec

@@ -18,12 +18,12 @@
       <group targetFramework=".NETFramework4.5">
         <dependency id="MaterialDesignColors" version="[1.2.1, 2.0)" />
         <dependency id="MaterialDesignThemes" version="[3.0.0, 4.0)" />
-        <dependency id="MahApps.Metro" version="[2.0.0-*,3.0)" />
+        <dependency id="MahApps.Metro" version="[2.0.0-alpha0660, 3.0)" />
       </group>
       <group targetFramework=".NETCoreApp3.1">
         <dependency id="MaterialDesignColors" version="[1.2.1, 2.0)" />
         <dependency id="MaterialDesignThemes" version="[3.0.0, 4.0)" />
-        <dependency id="MahApps.Metro" version="[2.0.0-*,3.0)" />
+        <dependency id="MahApps.Metro" version="[2.0.0-alpha0660, 3.0)" />
       </group>
     </dependencies>
   </metadata>