Bump Akka from 1.4.17 to 1.4.18 (#125)

Bumps [Akka](https://github.com/akkadotnet/akka.net) from 1.4.17 to 1.4.18.
- [Release notes](https://github.com/akkadotnet/akka.net/releases)
- [Changelog](https://github.com/akkadotnet/akka.net/blob/dev/RELEASE_NOTES.md)
- [Commits](akkadotnet/akka.net@1.4.17...1.4.18)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

src/common.props

@@ -24,7 +24,7 @@
     <NetCoreTestVersion>netcoreapp2.1</NetCoreTestVersion>
     <NetStandardVersion>netstandard2.0</NetStandardVersion>
     <NetFrameworkTestVersion>net461</NetFrameworkTestVersion>
-    <AkkaVersion>1.4.17</AkkaVersion>
+    <AkkaVersion>1.4.18</AkkaVersion>
     <SourceLinkVersion>1.0.0</SourceLinkVersion>
   </PropertyGroup>
 </Project>