fix start.sh to work on macos

[dgrove-oss]

remove extra leading / in volume mount command

Fixes #5016

[codecov-io]

Codecov Report

Merging #5019 into master will decrease coverage by 6.86%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5019      +/-   ##
==========================================
- Coverage   83.78%   76.91%   -6.87%     
==========================================
  Files         202      202              
  Lines        9786     9786              
  Branches      409      409              
==========================================
- Hits         8199     7527     -672     
- Misses       1587     2259     +672     

Impacted Files	Coverage Δ
...core/database/cosmosdb/RxObservableImplicits.scala	0.00% <0.00%> (-100.00%)	⬇️
...ore/database/cosmosdb/cache/CacheInvalidator.scala	0.00% <0.00%> (-100.00%)	⬇️
...e/database/cosmosdb/cache/ChangeFeedConsumer.scala	0.00% <0.00%> (-100.00%)	⬇️
...core/database/cosmosdb/CosmosDBArtifactStore.scala	0.00% <0.00%> (-95.85%)	⬇️
...sk/core/database/cosmosdb/CosmosDBViewMapper.scala	0.00% <0.00%> (-93.90%)	⬇️
...tabase/cosmosdb/cache/CacheInvalidatorConfig.scala	0.00% <0.00%> (-92.31%)	⬇️
...enwhisk/connector/kafka/KamonMetricsReporter.scala	0.00% <0.00%> (-83.34%)	⬇️
...e/database/cosmosdb/cache/KafkaEventProducer.scala	0.00% <0.00%> (-78.58%)	⬇️
...whisk/core/database/cosmosdb/CosmosDBSupport.scala	0.00% <0.00%> (-74.08%)	⬇️
...ore/database/azblob/AzureBlobAttachmentStore.scala	11.53% <0.00%> (-60.58%)	⬇️
... and 14 more

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