fix(gatsby-remark-images): Fix style-creation in gatsby-remark-images

[emilbruckner]

Remove unnecessary semicolon & don’t use null in String

When using rehype-react (as in Using remark: Custom components) together with gatsby-remark-images with options: showCaptions: true, sites crash, because the styles don’t make sense then. Even the old test-snapshot reflected that there would have been two semicolons, one after another.

That extra semicolon isn’t necessary, since added styles should contain their own semicolon anyway (See the plugin’s readme).

[emilbruckner]

I see that some snapshots don’t match on Environment: example=gatsbygram, buildon=commit.
Is that my fault? I don’t really understand where this change could be coming from

[pieh]

I see that some snapshots don’t match on Environment: example=gatsbygram, buildon=commit.
Is that my fault?

It's not your fault - one of previously merged PRs did add snapshot snapshot that contains file path (which will be different for windows and non-windows platforms). There are 2 alternative PRs with fix for that #8906 and #8836

[pieh]

Thanks @emilbruckner!

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