Adding error for caching POST requests

[gauntface]

Fixes #1223

Also added tests for checkSWFileCacheHeaders().

[workbox-pr-bot]

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View Table

File	Before	After	Change	GZipped
packages/workbox-background-sync/build/workbox-background-sync.prod.js	3.52 KB	3.52 KB	0%	1.45 KB
packages/workbox-broadcast-cache-update/build/workbox-broadcast-cache-update.prod.js	1.13 KB	1.13 KB	0%	589 B
packages/workbox-build/build/_types.js	41 B	41 B	0%	61 B
packages/workbox-build/build/index.js	2.52 KB	2.52 KB	0%	1.06 KB
packages/workbox-cache-expiration/build/workbox-cache-expiration.prod.js	3.41 KB	3.41 KB	0%	1.26 KB
packages/workbox-cacheable-response/build/workbox-cacheable-response.prod.js	594 B	594 B	0%	350 B
packages/workbox-cli/build/app.js	6.50 KB	6.50 KB	0%	2.16 KB
packages/workbox-cli/build/bin.js	2.32 KB	2.32 KB	0%	1.03 KB
packages/workbox-core/build/workbox-core.prod.js	6.48 KB	6.48 KB	0%	2.59 KB
packages/workbox-google-analytics/build/workbox-google-analytics.prod.js	2.13 KB	2.13 KB	0%	1.05 KB
packages/workbox-precaching/build/workbox-precaching.prod.js	5.26 KB	5.26 KB	0%	2.06 KB
packages/workbox-range-requests/build/workbox-range-requests.prod.js	1.64 KB	1.64 KB	0%	807 B
packages/workbox-routing/build/workbox-routing.prod.js	2.77 KB	2.77 KB	0%	1.25 KB
packages/workbox-strategies/build/workbox-strategies.prod.js	3.26 KB	3.26 KB	0%	1.02 KB
packages/workbox-sw/build/workbox-sw.js	1.46 KB	1.46 KB	0%	793 B
packages/workbox-webpack-plugin/build/generate-sw.js	7.38 KB	7.38 KB	0%	2.44 KB
packages/workbox-webpack-plugin/build/index.js	742 B	742 B	0%	470 B
packages/workbox-webpack-plugin/build/inject-manifest.js	8.96 KB	8.96 KB	0%	2.92 KB

Workbox Aggregate Size Plugin

☠️ WARNING ☠️

We are using 155% of our max size budget.

Total Size: 22.7KB
Percentage of Size Used: 155%

Gzipped: 9.1KB

[jeffposnick]

Looks good!