Add babel-runtime explicitly to deps

Was failing to build with:

Cannot find module 'babel-runtime/helpers/extends'
Require stack:
- /app/node_modules/react-leaflet-universal/dist/decorator.js
- /app/node_modules/react-leaflet-universal/dist/index.js
- /app/build/server.js
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:966:15)
    at Function.Module._load (internal/modules/cjs/loader.js:842:27)
    at Module.require (internal/modules/cjs/loader.js:1026:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at Object.<anonymous> (/home/tom/projects/colouring-london/colouring-london/app/node_modules/react-leaflet-universal/dist/decorator.js:7:17)
    at Module._compile (internal/modules/cjs/loader.js:1138:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1158:10)
    at Module.load (internal/modules/cjs/loader.js:986:32)
    at Function.Module._load (internal/modules/cjs/loader.js:879:14)
    at Module.require (internal/modules/cjs/loader.js:1026:19)

app/package-lock.json

@@ -3548,6 +3548,22 @@
         }
       }
     },
+    "babel-runtime": {
+      "version": "6.26.0",
+      "resolved": "https://registry.npmjs.org/babel-runtime/-/babel-runtime-6.26.0.tgz",
+      "integrity": "sha1-llxwWGaOgrVde/4E/yM3vItWR/4=",
+      "requires": {
+        "core-js": "^2.4.0",
+        "regenerator-runtime": "^0.11.0"
+      },
+      "dependencies": {
+        "regenerator-runtime": {
+          "version": "0.11.1",
+          "resolved": "https://registry.npmjs.org/regenerator-runtime/-/regenerator-runtime-0.11.1.tgz",
+          "integrity": "sha512-MguG95oij0fC3QV3URf4V2SDYGJhJnJGqvIIgdECeODCT98wSWDAJ94SSuVpYQUoTcGUIL6L4yNB7j1DFFHSBg=="
+        }
+      }
+    },
     "balanced-match": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/balanced-match/-/balanced-match-1.0.0.tgz",
@@ -4771,6 +4787,11 @@
       "integrity": "sha1-Z29us8OZl8LuGsOpJP1hJHSPV40=",
       "dev": true
     },
+    "core-js": {
+      "version": "2.6.11",
+      "resolved": "https://registry.npmjs.org/core-js/-/core-js-2.6.11.tgz",
+      "integrity": "sha512-5wjnpaT/3dV+XB4borEsnAYQchn00XSgTAWKDkEqv+K8KevjbzmofK6hfJ9TZIlpj2N0xQpazy7PiRQiWHqzWg=="
+    },
     "core-js-compat": {
       "version": "3.6.5",
       "resolved": "https://registry.npmjs.org/core-js-compat/-/core-js-compat-3.6.5.tgz",

app/package.json

@@ -17,6 +17,7 @@
     "@fortawesome/free-solid-svg-icons": "^5.13.0",
     "@fortawesome/react-fontawesome": "^0.1.9",
     "@mapbox/sphericalmercator": "^1.1.0",
+    "babel-runtime": "^6.26.0",
     "body-parser": "^1.19.0",
     "bootstrap": "^4.4.1",
     "connect-pg-simple": "^6.1.0",