fix: Fix "SLF4J: Failed to load ..." issue by adding slf4j-simple

[eed3si9n]

Fixes #931

Problem

sbt new raquo/scalajs.g8
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.

This is due to JGit adding slf4j-api but removed the binding at some point.

Solution

This adds slf4j-simple 1.7 to the depdency.