Make GetReferenceAssemblyPath pick the closest available version.

ICSharpCode.Decompiler/Metadata/DotNetCorePathFinder.cs

@@ -175,7 +175,9 @@ namespace ICSharpCode.Decompiler.Metadata
 				default:
 					throw new NotSupportedException();
 			}
-			return Path.Combine(dotnetBasePath, "packs", identifier + ".Ref", version.ToString(), "ref", identifierExt);
+			string basePath = Path.Combine(dotnetBasePath, "packs", identifier + ".Ref");
+			string versionFolder = GetClosestVersionFolder(basePath, version);
+			return Path.Combine(basePath, versionFolder, "ref", identifierExt);
 		}
 
 		static IEnumerable<DotNetCorePackageInfo> LoadPackageInfos(string depsJsonFileName, string targetFramework)
@@ -244,7 +246,7 @@ namespace ICSharpCode.Decompiler.Metadata
 			var foundVersions = new DirectoryInfo(basePath).GetDirectories()
 				.Select(d => ConvertToVersion(d.Name))
 				.Where(v => v.version != null);
-			foreach (var folder in foundVersions.OrderBy(v => v.Item1))
+			foreach (var folder in foundVersions.OrderBy(v => v.version))
 			{
 				if (folder.version >= version)
 					return folder.directoryName;