add support for macOS Big Sur (#70)

README.md

@@ -114,7 +114,7 @@ Unknown version is returned as `0`.
 
 #### OS Version
 
-OS X major version is alway 10 with consecutive minor versions indicating release releases (10 - Yosemite, 11 - El Capitain, 12 Sierra, etc). Windows version is NT version. `Version{0, 0, 0}` indicated version is unknown or not evaluated.
+OS X major version is always 10 for releases prior to Big Sur with consecutive minor versions indicating release releases (10 - Yosemite, 11 - El Capitain, 12 Sierra, etc). macOS Big Sur is indicated as `{11, 1, 0}`. Windows version is NT version. `Version{0, 0, 0}` indicated version is unknown or not evaluated.
 Versions can be compared using `Less` function: `if ver1.Less(ver2) {}`
 
 Here are some examples across the platform, os.name, and os.version:

system.go

@@ -233,7 +233,7 @@ func (u *UserAgent) evalWindows(ua string) {
 
 func (u *UserAgent) evalMacintosh(uaPlatformGroup string) {
 	u.OS.Platform = PlatformMac
-	if i := strings.Index(uaPlatformGroup, "os x 10"); i != -1 {
+	if i := strings.Index(uaPlatformGroup, "os x "); i != -1 {
 		u.OS.Name = OSMacOSX
 		u.OS.Version.parse(uaPlatformGroup[i+5:])
 

uasurfer_test.go

@@ -88,6 +88,10 @@ var testUAVars = []struct {
 		UserAgent{
 			Browser{BrowserSafari, Version{10, 0, 0}}, OS{PlatformMac, OSMacOSX, Version{10, 12, 0}}, DeviceComputer}},
 
+	{"Mozilla/5.0 (Macintosh; Intel Mac OS X 11_1_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36", // macOS Big Sur
+		UserAgent{
+			Browser{BrowserChrome, Version{87, 0, 4280}}, OS{PlatformMac, OSMacOSX, Version{11, 1, 0}}, DeviceComputer}},
+
 	// Firefox
 	{"Mozilla/5.0 (iPhone; CPU iPhone OS 8_3 like Mac OS X) AppleWebKit/600.1.4 (KHTML, like Gecko) FxiOS/1.0 Mobile/12F69 Safari/600.1.4",
 		UserAgent{