Fix chart logo URL

[u1735067]

Current URL seems not to be working (returning HTML content), and logo URL at https://landscape.cncf.io/?item=orchestration-management--scheduling-orchestration--stackstorm looks like it's generated (https://landscape.cncf.io/logos/57fe0fcfd8d465d0d0f5e819d3a99372d72512bdca0b648f1fa3b779ee515d42.svg ; I wasn't able to find if it's stable in time or not), so use raw URL from https://github.com/cncf/landscape/blob/master/hosted_logos/stackstorm.svg.

Maybe put a copy of the logo in this repo in the long-term?

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