Merge pull request #321 from adamkaplan/xcode10

[Swift 4] Fix not unwrapped optional value

Sources/HttpParser.swift

@@ -37,10 +37,10 @@ public class HttpParser {
             return []
         }
         let queryStart = url.index(after: questionMark)
-        guard url.endIndex > queryStart else {
-            return []
-        }
+
+        guard url.endIndex > queryStart else { return [] }
         let query = String(url[queryStart..<url.endIndex])
+
         return query.components(separatedBy: "&")
             .reduce([(String, String)]()) { (c, s) -> [(String, String)] in
                 guard let nameEndIndex = s.index(of: "=") else {