Backend: upgrade HtmlAgilityPack nuget dependency

The reason is that the new versions don't depend anymore on the
deprecated System.Net.Http nuget package. See [1] forr more info.

[1] dotnet/runtime#21777 (comment)

Author: knocte

src/GWallet.Backend/GWallet.Backend.fsproj

@@ -258,7 +258,7 @@
       <HintPath>..\..\packages\Nethereum.0.92.0-date20200610-0232.git-686865c\lib\netstandard2.0\Nethereum.Web3.dll</HintPath>
     </Reference>
     <Reference Include="HtmlAgilityPack">
-      <HintPath>..\..\packages\HtmlAgilityPack.1.11.9\lib\Net45\HtmlAgilityPack.dll</HintPath>
+      <HintPath>..\..\packages\HtmlAgilityPack.1.11.24\lib\Net45\HtmlAgilityPack.dll</HintPath>
     </Reference>
   </ItemGroup>
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 

src/GWallet.Backend/packages.config

@@ -3,7 +3,7 @@
   <package id="Common.Logging.Core" version="3.4.1" targetFramework="net46" />
   <package id="FSharp.Core" version="4.7.0" targetFramework="net461" />
   <package id="FSharp.Data" version="3.0.0" targetFramework="net46" />
-  <package id="HtmlAgilityPack" version="1.11.9" targetFramework="net46" />
+  <package id="HtmlAgilityPack" version="1.11.24" targetFramework="net471" />
   <package id="JsonRpcSharp" version="0.92.0-date20200610-0657.git-425436f" targetFramework="net461" />
   <package id="Microsoft.CSharp" version="4.0.1" targetFramework="net46" />
   <package id="Microsoft.Extensions.Logging.Abstractions" version="1.0.2" targetFramework="net46" />