This release contains multiple little improvements and compatibility fixes:

• Works with solc 0.4.21
• Use pending transaction nonce as default (allows to send multiple transactions within one block)
• Relaxed dependency to active record (allows to work with older active record versions)
• Now testing against ruby 2.3, 2.4 and 2.5
• Allow using a proxy for HttpClient
• Fix call payload for empty args
• Implement batch requests for HTTP client
• Support for truffle
• Updated readme