fix: do not initialize httpClient in MinioClient class level. (#633)
fix: do not initialize httpClient in MinioClient class level. (#633)

Previously httpClient was initialized at class level which causes
error with custom PKI implementation. In this situation any java
program using MinioClient (import io.minio.MinioClient;) would cause
failure.

This patch fixes the issue by initializing httpClient in constructor
level

Fixes #628
balamurugana/minio-java,vadmeste/minio-java,minio/minio-java