bug: Documentation should show esbuildOptions, not esbuildBuildOptions

[tbuckley]

Describe the Bug

The documentation in README.md guides users to use esbuildBuildOptions to configure esbuild. However the code actually uses esbuildOptions : https://github.com/jthegedus/svelte-adapter-firebase/blob/main/src/index.js#L20

Steps to Reproduce

1. Add esbuildBuildOptions configuration to svelte.config.js, eg adding target: "esm"

Expected Behaviour

The configuration options should apply

svelte-adapter-firebase version

0.15.0

sveltejs/kit version

1.7.2