Update Polly.Caching.Memory.nuspec

Updated netstandard2.0 Polly v7.0.0 reference to Polly v7.0.2.

Author: joelhulen

src/Polly.Caching.Memory.nuspec

@@ -63,7 +63,7 @@
         <dependency id="System.ValueTuple" version="4.5.0" />
       </group>
       <group targetFramework="netstandard2.0">
-        <dependency id="Polly" version="7.0.0" />
+        <dependency id="Polly" version="7.0.2" />
         <dependency id="Microsoft.Extensions.Caching.Memory" version="2.0.2" />
       </group>
     </dependencies>