Added move assignment operator to Client class. (#1873)

httplib.h

@@ -1530,6 +1530,7 @@ public:
                   const std::string &client_key_path);
 
   Client(Client &&) = default;
+  Client &operator=(Client &&) = default;
 
   ~Client();
 

test/test.cc

@@ -54,11 +54,17 @@ MultipartFormData &get_file_value(MultipartFormDataItems &files,
 #endif
 }
 
-TEST(ConstructorTest, MoveConstructible) {
+TEST(ClientTest, MoveConstructible) {
   EXPECT_FALSE(std::is_copy_constructible<Client>::value);
   EXPECT_TRUE(std::is_nothrow_move_constructible<Client>::value);
 }
 
+TEST(ClientTest, MoveAssignable)
+{
+    EXPECT_FALSE(std::is_copy_assignable<Client>::value);
+    EXPECT_TRUE(std::is_nothrow_move_assignable<Client>::value);
+}
+
 #ifdef _WIN32
 TEST(StartupTest, WSAStartup) {
   WSADATA wsaData;