Typos fixed (#474)

Author: Saika Fatih

httplib.h

@@ -241,18 +241,18 @@ class ContentReader {
   using MultipartReader = std::function<bool(MultipartContentHeader header,
                                              ContentReceiver receiver)>;
 
-  ContentReader(Reader reader, MultipartReader muitlpart_reader)
-      : reader_(reader), muitlpart_reader_(muitlpart_reader) {}
+  ContentReader(Reader reader, MultipartReader multipart_reader)
+      : reader_(reader), multipart_reader_(multipart_reader) {}
 
   bool operator()(MultipartContentHeader header,
                   ContentReceiver receiver) const {
-    return muitlpart_reader_(header, receiver);
+    return multipart_reader_(header, receiver);
   }
 
   bool operator()(ContentReceiver receiver) const { return reader_(receiver); }
 
   Reader reader_;
-  MultipartReader muitlpart_reader_;
+  MultipartReader multipart_reader_;
 };
 
 using Range = std::pair<ssize_t, ssize_t>;