Squashed 'lib/riskified_php_sdk/' changes from 41a5f5e..71f12f4

71f12f4 update decision notification to v2 add migration info to README
54d4377 change http headers to hyphens

git-subtree-dir: lib/riskified_php_sdk
git-subtree-split: 71f12f4b8791522584e462589a4d94394ae6e714
updating riskified_php_sdk to v1.0.3