Incomplete standard output

I have come across a scenario when not all standard output is returned. This seems to be happening on a non zero exit code, successful termination may or may not be affected.

**Background**
I was using shellOut to execute fastlane and it was failing for version requirements not being read.

**Investigation**
I did some tinkering and it seems to be related to how this function reads the output.

```swift
private extension Process {
@discardableResult func launchBash(with command: String, outputHandle: FileHandle? = nil, errorHandle: FileHandle? = nil) throws -> String {
launchPath = "/bin/bash"
arguments = ["-c", command]

var outputData = Data()
var errorData = Data()

let outputPipe = Pipe()
standardOutput = outputPipe

let errorPipe = Pipe()
standardError = errorPipe

#if !os(Linux)
outputPipe.fileHandleForReading.readabilityHandler = { handler in
let data = handler.availableData
outputData.append(data)
outputHandle?.write(data)
}

errorPipe.fileHandleForReading.readabilityHandler = { handler in
let data = handler.availableData
errorData.append(data)
errorHandle?.write(data)
}
#endif

launch()

#if os(Linux)
outputData = outputPipe.fileHandleForReading.readDataToEndOfFile()
errorData = errorPipe.fileHandleForReading.readDataToEndOfFile()
#endif

waitUntilExit()

outputHandle?.closeFile()
errorHandle?.closeFile()

#if !os(Linux)
outputPipe.fileHandleForReading.readabilityHandler = nil
errorPipe.fileHandleForReading.readabilityHandler = nil
#endif

if terminationStatus != 0 {
throw ShellOutError(
terminationStatus: terminationStatus,
errorData: errorData,
outputData: outputData
)
}

return outputData.shellOutput()
}
}
```

This is the output when using the default implementation

```
[19:08:21]: -------------------------------------------------
[19:08:21]: --- Step: Verifying required fastlane version ---
[19:08:21]: -------------------------------------------------
```

I noticed the linux only variation and thought I would try it out on macos, I hacked the function as follows.

```swift
private extension Process {
@discardableResult func launchBash(with command: String, outputHandle: FileHandle? = nil, errorHandle: FileHandle? = nil) throws -> String {
launchPath = "/bin/bash"
arguments = ["-c", command]

var outputData = Data()
var errorData = Data()

let outputPipe = Pipe()
standardOutput = outputPipe

let errorPipe = Pipe()
standardError = errorPipe

// #if !os(Linux)
// outputPipe.fileHandleForReading.readabilityHandler = { handler in
// let data = handler.availableData
// outputData.append(data)
// outputHandle?.write(data)
// }

// errorPipe.fileHandleForReading.readabilityHandler = { handler in
// let data = handler.availableData
// errorData.append(data)
// errorHandle?.write(data)
// }
// #endif

launch()

// #if os(Linux)
outputData = outputPipe.fileHandleForReading.readDataToEndOfFile()
errorData = errorPipe.fileHandleForReading.readDataToEndOfFile()
// #endif

waitUntilExit()

outputHandle?.closeFile()
errorHandle?.closeFile()

#if !os(Linux)
outputPipe.fileHandleForReading.readabilityHandler = nil
errorPipe.fileHandleForReading.readabilityHandler = nil
#endif

if terminationStatus != 0 {
throw ShellOutError(
terminationStatus: terminationStatus,
errorData: errorData,
outputData: outputData
)
}

return outputData.shellOutput()
}
}
```

Which produces the following output
```
[19:04:50]: -------------------------------------------------
[19:04:50]: --- Step: Verifying required fastlane version ---
[19:04:50]: -------------------------------------------------

[!] The Fastfile requires a fastlane version of >= 2.47.0. You are on 1.91.0. Please update using `sudo gem update fastlane`.
```

Assuming I am not using this wrong it looks like the output is getting cut off early.