fin-ocr-cli generates bad images

## Bug Report

### Steps to Reproduce:
1. clone and build fin-ocr-cli
2. run `./scripts/ocr check generate 1`
3. run `./scripts/ocr check scan ~/.fin-ocr/checks/check-1.png`

### Expected Result:
User should see a JSON data structures containing the generated check information. Something like:
```
{
"id": "/Users/aaron/.fin-ocr/checks/check-1.png",
"translators": {
"tesseract": {
"result": {
"micrLine": "[aoe 2 ete eee ie. - Lee Se\n",
"routingNumber": "",
"accountNumber": "",
"checkNumber": ""
}
},
"opencv": {
"result": {
"micrLine": "T751116251T259233723U4437",
"routingNumber": "751116251",
"accountNumber": "259233723",
"checkNumber": "4437"
}
}
},
"overlap": true
}
```

### Actual Result:
```
Sending scan request for ID: /Users/aaron/.fin-ocr/checks/check-1.png
Error processing file /Users/aaron/.fin-ocr/checks/check-1.png: Error: Failed to decode image/png: unrecognised content at end of stream
at Util.bufferToMat (file:///Users/aaron/crap/fin-ocr-sdk/build/src/util.js:38:19)
at Image.fromBuffer (file:///Users/aaron/crap/fin-ocr-sdk/build/src/image.js:52:26)
at Check.getMicrLine (file:///Users/aaron/crap/fin-ocr-sdk/build/src/check.js:158:25)
at Check.scan (file:///Users/aaron/crap/fin-ocr-sdk/build/src/check.js:41:37)
at CheckMgr.getScanResponse (file:///Users/aaron/crap/fin-ocr-cli/build/check.js:271:42)
at CheckMgr.scan (file:///Users/aaron/crap/fin-ocr-cli/build/check.js:203:31)
at checkScan (file:///Users/aaron/crap/fin-ocr-cli/build/main.js:134:41)
at async check (file:///Users/aaron/crap/fin-ocr-cli/build/main.js:51:13)
at async main (file:///Users/aaron/crap/fin-ocr-cli/build/main.js:32:9)
```

### Environment:
Issue noticed on fin-ocr-cli main yesterday using fin-ocr-sdk@1.0.5