Fix build on non Unix platforms

[gentlementlegen]

          This broke builds on Windows (sorry if I am the only hipster here). `cat` command is only Unix compliant. I'd suggest using cross platform commands or directly Node which is sure to run on any platform. Guilty code:

pay.ubq.fi/build/esbuild-build.ts

Line 30 in ec2fd20

execSync(`cat static/styles/rewards/pay.css > static/bundles/bundles.css`);

Originally posted by @gentlementlegen in #278 (comment)

[hhio618]

/start

[ubiquity-os]

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[ 25 WXDAI ]

@hhio618

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Resolves #282 <!-- - You must link the issue number e.g. "…	0 content: p: count: 3 score: 1 ul: count: 18 score: 0 li: count: 18 score: 1 wordValue: 0 formattingMultiplier: 0	0.3	-

[ 13.8 WXDAI ]

@gentlementlegen

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This broke builds on Windows (sorry if I am the only hipster her…	13.8 content: p: count: 45 score: 1 code: count: 1 score: 1 em: count: 6 score: 0 wordValue: 0.1 formattingMultiplier: 3	1	13.8

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@gitcoindev

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Looks clean to me. fsWriteFileSync is cross platform and automat…	0.675 content: p: count: 26 score: 1 code: count: 1 score: 1 wordValue: 0.1 formattingMultiplier: 0.25	1	0.675

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@0x4007

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Makes sense to use type script instead of the shell	1 content: p: count: 10 score: 1 wordValue: 0.1 formattingMultiplier: 1	1	1

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@Keyrxng

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This workflow failed earlier because it hit a secondary rate lim…	1.6 content: p: count: 16 score: 1 wordValue: 0.1 formattingMultiplier: 1	1	1.6