Ruby: explicitly require 'grpc/grpc' when loading C core, to avoid circular import warning

src/ruby/lib/grpc/core/time_consts.rb

@@ -27,7 +27,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-require 'grpc'
+require 'grpc/grpc'
 
 # GRPC contains the General RPC module.
 module GRPC

src/ruby/lib/grpc/errors.rb

@@ -27,7 +27,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-require 'grpc'
+require 'grpc/grpc'
 
 # GRPC contains the General RPC module.
 module GRPC