repair typo in nuspec

Author: lmagyar

src/Orleans.Activities/Orleans.Activities.nuspec

@@ -22,7 +22,7 @@
     </frameworkAssemblies>
     <dependencies>
       <group targetFramework="net461">
-        <dependency id="Microsoft.Orleans.Core" version="[1.5.3,2.0.0)" targetFramework="net461" />
+        <dependency id="Microsoft.Orleans.Core" version="[1.5.3,2.0.0)" />
       </group>
     </dependencies>
   </metadata>