Fix gas estimation harcoding it

[pmprete]

Gas estimation does not work correctly on RSK and after the London harfork, neither is working on Ethereum
Example https://etherscan.io/tx/0xd30d6cf428606e2ef3667427b9b6baecb2f4c9cbb44a0c82c735a238ec8f72fb
To fix it, we decided to use a hardcoded gas estimation of 250.000

Also Lucas informed me that we got this error

[2021-08-17T14:44:18.687] [INFO] HEARTBEAT - Found 9 heartbeatLogs
TypeError [ERR_INVALID_ARG_TYPE]: The "data" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received type number (3609055)
    at Object.writeFileSync (node:fs:2136:5)
    at Heartbeat._saveProgress (/app/federator/src/lib/Heartbeat.js:213:16)
    at Heartbeat.readLogs (/app/federator/src/lib/Heartbeat.js:127:26)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async run (/app/federator/src/main.js:52:9)
    at async Scheduler.poll (/app/federator/src/services/Scheduler.js:24:13)
    at async Scheduler.start (/app/federator/src/services/Scheduler.js:17:9) {
  code: 'ERR_INVALID_ARG_TYPE'
}
[2021-08-17T14:44:18.687] [ERROR] HEARTBEAT - Error: Exception Running Federator
    at Heartbeat.readLogs (/app/federator/src/lib/Heartbeat.js:134:35)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async run (/app/federator/src/main.js:52:9)
    at async Scheduler.poll (/app/federator/src/services/Scheduler.js:24:13)
    at async Scheduler.start (/app/federator/src/services/Scheduler.js:17:9) TypeError [ERR_INVALID_ARG_TYPE]: The "data" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received type number (3609055)
    at Object.writeFileSync (node:fs:2136:5)
    at Heartbeat._saveProgress (/app/federator/src/lib/Heartbeat.js:213:16)
    at Heartbeat.readLogs (/app/federator/src/lib/Heartbeat.js:127:26)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async run (/app/federator/src/main.js:52:9)
    at async Scheduler.poll (/app/federator/src/services/Scheduler.js:24:13)
    at async Scheduler.start (/app/federator/src/services/Scheduler.js:17:9) {
  code: 'ERR_INVALID_ARG_TYPE'
}```
The error is that writeFileSync does not support passing a number from this size, so we need to convert it to a string
``` fs.writeFileSync(path, value.toString());```

[lgtm-com]

This pull request introduces 1 alert when merging bcacedc into 591403c - view on LGTM.com

new alerts:

• 1 for Incomplete URL substring sanitization