fix: Restore compatibility with Linux with missing hasPrefix

Closes #56

Author: kylef

CHANGELOG.md

@@ -9,6 +9,10 @@
   - All Option-related types now have a flag parameter.
   - All constructors have the same constructor arguments order. [#35](https://github.com/kylef/Commander/issues/35)
 
+### Bug Fixes
+
+- Restores compatibility with Linux.
+
 ## 0.7.1
 
 ### Bug Fixes

Sources/Commander/ArgumentParser.swift

@@ -54,10 +54,10 @@ public final class ArgumentParser : ArgumentConvertible, CustomStringConvertible
   /// Initialises the ArgumentParser with an array of arguments
   public init(arguments: [String]) {
     self.arguments = arguments.map { argument in
-      if argument.hasPrefix("-") {
+      if argument.first == "-" {
         let flags = argument[argument.index(after: argument.startIndex)..<argument.endIndex]
 
-        if flags.hasPrefix("-") {
+        if flags.first == "-" {
           let option = flags[flags.index(after: flags.startIndex)..<flags.endIndex]
           return .option(String(option))
         }