build(tap): run tests with 4 GB JS heap

Necessary because with the addition of the
cactus-example-* packages the footprint
of the code has grown to the point where
2 GB default heap size is not cutting it
anymore apparently.
See example of a crash due to lack of
available memory here:
https://travis-ci.org/github/hyperledger/cactus/jobs/739153212#L10922

Signed-off-by: Peter Somogyvari <peter.somogyvari@accenture.com>

package.json

@@ -38,10 +38,10 @@
     "webpack:prod": "lerna run webpack:prod",
     "webpack:prod:web": "lerna run webpack:prod:web",
     "webpack:prod:node": "lerna run webpack:prod:node",
-    "test:all": "tap --jobs=1 --timeout=600 \"packages/cactus-*/src/test/typescript/{unit,integration}/\"",
-    "test:unit": "tap --timeout=600 \"packages/cactus-*/src/test/typescript/unit/\"",
+    "test:all": "tap --node-arg=--max-old-space-size=4096 --jobs=1 --timeout=600 \"packages/cactus-*/src/test/typescript/{unit,integration}/\"",
+    "test:unit": "tap --node-arg=--max-old-space-size=4096 --timeout=600 \"packages/cactus-*/src/test/typescript/unit/\"",
     "test:browser": "karma start karma.conf.js",
-    "test:integration": "tap --jobs=1 --timeout=600 \"packages/cactus-*/src/test/typescript/integration/\"",
+    "test:integration": "tap --node-arg=--max-old-space-size=4096 --jobs=1 --timeout=600 \"packages/cactus-*/src/test/typescript/integration/\"",
     "changelog": "conventional-changelog --infile CHANGELOG.md --outfile CHANGELOG.md && git add CHANGELOG.md",
     "commit": "git-cz --signoff",
     "prettier": "prettier --write --config .prettierrc.json \"./**/*.{ts,js}\"",