Fix solc-nightly job (#1732)

* update truffle to 5.0.14

* fix setup to test with solc-nightly

* switch to npx in script/test.sh

* please the linter

* rename build to prepack

* move download of nightly build to a compile script

* make compile script executable

scripts/prepack.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+# Configure to exit script as soon as a command fails.
+set -o errexit
+
+# Clean the existing build directory.
+rm -rf build
+
+# Create a temporary directory to place ignored files (e.g. examples).
+tmp_dir="ignored_contracts"
+mkdir "$tmp_dir"
+
+# Move the ignored files to the temporary directory.
+while IFS="" read -r ignored
+do
+  mv "contracts/$ignored" "$tmp_dir"
+done < contracts/.npmignore
+
+# Compile everything else.
+npm run compile
+
+# Return ignored files to their place.
+mv "$tmp_dir/"* contracts/
+
+# Delete the temporary directory.
+rmdir "$tmp_dir"