add constructor to GsonMappingProvider that takes a GsonBuilder #157

	---
	name: Java CI

	on:
	push:
	pull_request:

	jobs:
	test:
	runs-on: ubuntu-latest
	strategy:
	matrix:
	java: [8, 11, 17, 18]
	fail-fast: false
	max-parallel: 4
	name: JDK ${{ matrix.java }}

	steps:
	- uses: actions/checkout@v2
	- name: Set up JDK
	uses: actions/setup-java@v1
	with:
	java-version: ${{ matrix.java }}
	- name: Grant execute permission for gradlew
	run: chmod +x gradlew

	- name: Build with Gradle
	run: ./gradlew build --warning-mode all

	- name: Run Tests
	run: ./gradlew check

	- name: Maven Install
	run: ./gradlew clean publishToMavenLocal

	...

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