fix: retry caldav init at startup

vendor/github.com/avast/retry-go/.gitignore

@@ -0,0 +1,21 @@
+# Binaries for programs and plugins
+*.exe
+*.dll
+*.so
+*.dylib
+
+# Test binary, build with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Project-local glide cache, RE: https://github.com/Masterminds/glide/issues/736
+.glide/
+
+# dep
+vendor/
+Gopkg.lock
+
+# cover
+coverage.txt