fetch error logging to use warn instead of error

[victorlpgazolli]

Simple change from console.error to console.warn in .fetch method

motivation:
Users with no internet access can cause fetch to throw errors, this can be seen by these errors messages:

• "Request timeout after 10000 milliseconds"
• "Network request failed"

When this sdk is integrated with an app that uses sentry, handling this error with console.error can flood sentry issues with users who has internet related problems (timeout or unreachable network).

One way to handle this kind of error would be to check for response.status === 0, and ignore this internet related error.
BUT this pull request suggest an 'one-liner' approach (nothing sofisticated, just a workaround).

Other way (arguably the best way) would be to just throw this exception, and let it break. So the developer (user of this sdk) can handle this kind of error. I would like to see this implementation :)

tldr;
@amplitude/experiment-react-native-client flooding Sentry platform with "Network request failed" and "Request timeout after 10000 milliseconds" with this "console.error"

[victorlpgazolli]

Btw, i follow this Issue:
#9 (comment)

But the recommendations don't seem to fix the root problem