Use --reject for nimble install ntangle

Author: kaushalmodi

.travis.yml

@@ -68,8 +68,10 @@ script:
   # Compile the static binary using musl.
   # --accept to say Yes to prompts like "Prompt: No local packages.json found, download it from internet? [y/N]"
   - nimble install --depsOnly --accept
-  # Test installing ntangle using nimble
-  - nimble install --accept ntangle
+  # Test installing ntangle using nimble.
+  # --reject denies the offer to install from ntangle@#head if "nimble install ntangle" fails.
+  - nimble install --reject ntangle
+  # Now build using musl.
   - git clone https://github.com/kaushalmodi/nim_config && cp nim_config/config.nims . # Get my global config.nims
   - nim musl "${NIMFILE}"
   # Verify the built binary version.