Update httparty to get rid of faulty dependency multi_xml (0.7.1)

> Your bundle is locked to multi_xml (0.7.1) from rubygems repository
https://rubygems.org/ or installed locally, but that version can no longer be
found in that source. That means the author of multi_xml (0.7.1) has removed it.

Gemfile.lock

@@ -18,7 +18,6 @@ GEM
       public_suffix (>= 2.0.2, < 6.0)
     ast (2.4.2)
     base64 (0.2.0)
-    bigdecimal (3.1.8)
     byebug (11.1.3)
     coderay (1.1.3)
     concurrent-ruby (1.2.2)
@@ -45,8 +44,7 @@ GEM
     method_source (1.0.0)
     mini_mime (1.1.5)
     minitest (5.18.0)
-    multi_xml (0.7.1)
-      bigdecimal (~> 3.1)
+    multi_xml (0.6.0)
     parallel (1.22.1)
     parser (3.2.2.0)
       ast (~> 2.4.1)