Can't build gem, bundler won't install

[rutgerrrrr]

Hi, whenever I build this gem, bundler won't install it and throws me this error:

[!] There was an error parsing shopify_theme-0.0.25.gem: Undefined local variable or method `metadata' for Gemfile. Bundler cannot continue.

from /Users/Rutger/Downloads/shopify_theme-master/pkg/shopify_theme-0.0.25.gem:1

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metadata.gz0000444000000000000000000000140013010374017013425 0ustar00wheelwheel00000000000000?!X?X?o?0~?a????cCS$&?HH?!@(r?K??????????9;??nӨSjZ%?????/????hD??vڍ????ހʲ??(g^M4S?QW?F?]?kP@f??n????E(?rJ?4?; ?d?4Ve4t"????.##??Ԛ?e????VX?I?B?f????9??@???H?<z쥓??d??4??7I/??Ѐ.@s1?M?Ǘ2?hac??@????qqW?1T???s?b'6B?.??cI??~??v?5H)???????Ash.?t?P:?)?k?{?0뻿??ϣ??~????8?????y?>6?{?kj?p4?U?o?ű??>??+?Ҷ?k:?KW?(???zq??FQ??%??t??r?0s-Bc%?????u>??o????i??????mJ?lJϸ?J|O?8nE??Q??J??zc$?h

?e?H??f?@? ?`)?C5???C??????XW??

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I'm by no means experienced with Ruby but if someone could show me the steps to build, that would be great.