v2.4.0

• feat(action): Allow action return void.
• feat(getActions): Add actions getter standalone.
• fix(connect): Feed the missed props.
• fix(connect): Resolve the conflict issue when use multi connects.
• feat(class): Add Class components' middleware support.
• fix(compatiable): React > 16.3.0.
• fix(type): Fix TSLint error in helper.ts.
• feat(robot): Greenkeeper enabled.
• style(comment,type): Improve the source code's readability.
• ci(Travis): Improve Code Coverage and Add codecov.
• test(init): Add ts-jest for testing.