Improve 'command took' log line format

Author: AndreyAkinshin

src/BenchmarkDotNet/Extensions/DoubleExtensions.cs

@@ -0,0 +1,10 @@
+using System.Globalization;
+
+namespace BenchmarkDotNet.Extensions
+{
+    internal static class DoubleExtensions
+    {
+        public static string ToInvariantString(this double value) => value.ToString(CultureInfo.InvariantCulture);
+        public static string ToInvariantString(this double value, string format) => value.ToString(format, CultureInfo.InvariantCulture);
+    }
+}

src/BenchmarkDotNet/Toolchains/DotNetCli/DotNetCliCommandExecutor.cs

@@ -46,7 +46,7 @@ public static DotNetCliCommandResult Execute(DotNetCliCommand parameters)
                 stopwatch.Stop();
                 outputReader.StopRead();
 
-                parameters.Logger.WriteLineInfo($"// command took {stopwatch.Elapsed.TotalSeconds:0.##}s and exited with {process.ExitCode}");
+                parameters.Logger.WriteLineInfo($"// command took {stopwatch.Elapsed.TotalSeconds.ToInvariantString("0.##")} sec and exited with {process.ExitCode}");
 
                 return process.ExitCode <= 0
                     ? DotNetCliCommandResult.Success(stopwatch.Elapsed, outputReader.GetOutputText())