Upgrade isomorphic-git to incorporate patch for properly handling network error
If a network error occurred (such as ECONNRESET) while reading the git-upload-pack response, isomorphic-git would print the error to STDOUT then continue on. This behavior would mask the probably and typically lead to an incoherent error later in the program flow. Antora is unable to deal with the error in this circumstance. This problem has since been addressed in isomorphic-git. See https://github.com/isomorphic-git/isomorphic-git/issues/1847. By upgrading isomorphic-git in Antora, we can avoid network errors going directly to STDOUT and be able to rely the network error to the user.
As part of this upgrade, include the reason (the network error) in the log message when Antora retries any failed fetch/clone operations in serial (related to #1096 (closed)).