Add 20% to gas price estimation from RPC

[sveitser]

This should make it unlikely that our transactions are ignored.

[philippecamacho]

Just had one test failing:

failures:

---- backend::test::test_anonymous_erc20_transfer stdout ----
Sent funding tx to deployer
xfr: 987 bytes
mint: 971 bytes
freeze: 979 bytes
Sent funding tx to deployer
thread 'backend::test::test_anonymous_erc20_transfer' panicked at 'called `Result::unwrap()` on an `Err` value: Failed { msg: "relayer error: response body fails to deserialize: io error: unexpected end of file" }', wallet/src/backend.rs:1004:14
stack backtrace:
   0: rust_begin_unwind
             at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/core/src/panicking.rs:142:14
   2: core::result::unwrap_failed
             at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/core/src/result.rs:1805:5
   3: cape_wallet::backend::test::test_anonymous_erc20_transfer::{{closure}}
   4: std::thread::local::LocalKey<T>::with
   5: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
   6: async_io::driver::block_on
   7: async_global_executor::reactor::block_on
   8: std::thread::local::LocalKey<T>::with
   9: std::thread::local::LocalKey<T>::with
  10: async_std::task::builder::Builder::blocking
  11: core::ops::function::FnOnce::call_once
  12: core::ops::function::FnOnce::call_once
             at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/core/src/ops/function.rs:248:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

failures:
    backend::test::test_anonymous_erc20_transfer

test result: FAILED. 14 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 69.95s

error: test failed, to rerun pass '-p cape_wallet --lib'
Sending HUP signal to run-geth: 27432
Cleaning up geth node
Removing geth data dir /run/user/1000/cap-ethereum-data-lWzf5ATu

[sveitser]

Same error as in

• 1179

[philippecamacho]

Same error as in

• backend::test::test_anonymous_erc20_transfer fails with response body fails to deserialize #1179

After uninstalling rust on my machine the tests pass.