pkg/units: Updated `Compile()` to `MustCompile()`

We were doing exactly what `regexp.MustCompile()` already does.

Docker-DCO-1.1-Signed-off-by: fcarriedo <fcarriedo@gmail.com> (github: fcarriedo)

pkg/units/size.go

@@ -15,10 +15,7 @@ const (
 var sizeRegex *regexp.Regexp
 
 func init() {
-	var err error
-	if sizeRegex, err = regexp.Compile("^(\\d+)([kKmMgGtTpP])?[bB]?$"); err != nil {
-		panic("Failed to compile the 'size' regular expression")
-	}
+	sizeRegex = regexp.MustCompile("^(\\d+)([kKmMgGtTpP])?[bB]?$")
 }
 
 var bytePrefixes = [...]string{"B", "kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB"}