Make path comparison case insensitive

On one mac os x system, the directory is reported as /Users/username/exercism in one place
and /users/username/exercism in another. Since both mac and windows are case insensitive in terms
of creating directories on a system (cannot have Hello and hello in the same location), lowercasing
both the filename and the directory before comparing them seems like a fairly innocuous approach.

api/iteration.go

@@ -37,7 +37,7 @@ func (iter *Iteration) RelativePath() string {
 
 // Identify attempts to determine the track and problem of an iteration.
 func (iter *Iteration) Identify() error {
-	if !strings.HasPrefix(iter.File, iter.Dir) {
+	if !strings.HasPrefix(strings.ToLower(iter.File), strings.ToLower(iter.Dir)) {
 		return fmt.Errorf(msgUnidentifiable)
 	}
 

api/iteration_test.go

@@ -19,6 +19,10 @@ func TestIdentify(t *testing.T) {
 			file: "/Users/me/exercism/bob.rb",
 			ok:   false,
 		},
+		{
+			file: "/users/me/exercism/ruby/bob/bob.rb",
+			ok:   true,
+		},
 		{
 			file: "/Users/me/bob.rb",
 			ok:   false,