Add macOS Catalina support in OsBrandStringHelper

Author: AndreyAkinshin

src/BenchmarkDotNet/Environments/OsBrandStringHelper.cs

@@ -200,7 +200,8 @@ private MacOSXVersion(int darwinVersion, [NotNull] string codeName)
                 new MacOSXVersion(15, "El Capitan"),
                 new MacOSXVersion(16, "Sierra"),
                 new MacOSXVersion(17, "High Sierra"),
-                new MacOSXVersion(18, "Mojave")
+                new MacOSXVersion(18, "Mojave"),
+                new MacOSXVersion(19, "Catalina")
             };
 
             [CanBeNull]

tests/BenchmarkDotNet.Tests/Environments/OsBrandStringTests.cs

@@ -48,6 +48,7 @@ public void WindowsWithUbrIsPrettified(string originalVersion, int ubr, string p
         [Theory]
         [InlineData("macOS 10.12.6 (16G29)", "Darwin 16.7.0", "macOS Sierra 10.12.6 (16G29) [Darwin 16.7.0]")]
         [InlineData("macOS 10.13.4 (17E199)", "Darwin 17.5.0", "macOS High Sierra 10.13.4 (17E199) [Darwin 17.5.0]")]
+        [InlineData("macOS 10.15.4 (19E266)", "Darwin 19.4.0", "macOS Catalina 10.15.4 (19E266) [Darwin 19.4.0]")]
         public void MacOSXIsPrettified(string systemVersion, string kernelVersion, string prettifiedName)
             => Check(OsBrandStringHelper.PrettifyMacOSX(systemVersion, kernelVersion), prettifiedName);
     }