Fixed: macOS version detection

(cherry picked from commit 060be6177a5477c94823e6a423c42064dedc1afb)

src/NzbDrone.Mono.Test/EnvironmentInfo/VersionAdapters/MacOsVersionAdapterFixture.cs

@@ -15,6 +15,9 @@ namespace NzbDrone.Mono.Test.EnvironmentInfo.VersionAdapters
         [TestCase("10.8")]
         [TestCase("10.8.1")]
         [TestCase("10.11.20")]
+        [TestCase("11.7.9")]
+        [TestCase("12.6.8")]
+        [TestCase("13.5.1")]
         public void should_get_version_info(string versionString)
         {
             var fileContent = File.ReadAllText(GetTestPath("Files/macOS/SystemVersion.plist")).Replace("10.0.0", versionString);

src/NzbDrone.Mono/EnvironmentInfo/VersionAdapters/MacOsVersionAdapter.cs

@@ -10,7 +10,7 @@ namespace NzbDrone.Mono.EnvironmentInfo.VersionAdapters
     {
         private const string PLIST_DIR = "/System/Library/CoreServices/";
 
-        private static readonly Regex DarwinVersionRegex = new Regex("<string>(?<version>10\\.\\d{1,2}\\.?\\d{0,2}?)<\\/string>",
+        private static readonly Regex DarwinVersionRegex = new ("<key>ProductVersion<\\/key>\\s*<string>(?<version>1\\d\\.\\d{1,2}\\.?\\d{0,2}?)<\\/string>",
             RegexOptions.Compiled | RegexOptions.IgnoreCase);
 
         private readonly IDiskProvider _diskProvider;