build: don't fail coverage from untrusted forks

The CircleCI tool by default will not expose secrets to untrusted
forks in the ci build. In this case, that means that
`$CODACY_PROJECT_TOKEN` is not set before the build, and the final
step of the CI build is to send Codacy coverage data. This change
prevents this from causing a build failure when the variable is
unset due to a PR from an untrusted fork (i.e. the community).

package.json

@@ -19,7 +19,7 @@
     "test": "nyc tape test/*.js | tap-spec",
     "test:headless": "node test/browser/webpack-test.js",
     "test:browser": "opener http://localhost:9007/test/browser/index.html && serve . -p 9007",
-    "coverage": "nyc report && nyc report --reporter=text-lcov | codacy-coverage",
+    "coverage": "nyc report && if [ $CODACY_PROJECT_TOKEN'' != '' ] ; then nyc report --reporter=text-lcov | codacy-coverage; fi",
     "ci": "npm run build && npm run test && npm run test:headless && npm run coverage",
     "prerelease": "npm run test:ci",
     "release": "standard-version -s",