build: force jest@25

Since ts-jest has not yet adopted jest@26.

Author: cuebit

package.json

@@ -66,7 +66,7 @@
     "conventional-changelog-cli": "^2.0.31",
     "enquirer": "^2.3.5",
     "execa": "^4.0.0",
-    "jest": "^26.0.0",
+    "jest": "25.5.4",
     "prettier": "1.19.1",
     "rollup": "^2.7.6",
     "rollup-plugin-terser": "^5.3.0",