[misc] install bunyan as production dependency

```
Error: Cannot find module 'bunyan'
Require stack:
- .../node_modules/@google-cloud/logging-bunyan/build/src/middleware/express.js
- .../node_modules/@google-cloud/logging-bunyan/build/src/index.js
- .../node_modules/logger-sharelatex/logging-manager.js
- .../node_modules/logger-sharelatex/index.js
- .../app.js
```

services/docstore/package-lock.json

@@ -1794,9 +1794,9 @@
       "integrity": "sha512-lGzLKcioL90C7wMczpkY0n/oART3MbBa8R9OFGE1rJxoVI86u4WAGfEk8Wjv10eKSyTHVGkSo3bvBylCEtk7LA=="
     },
     "bunyan": {
-      "version": "1.8.14",
-      "resolved": "https://registry.npmjs.org/bunyan/-/bunyan-1.8.14.tgz",
-      "integrity": "sha512-LlahJUxXzZLuw/hetUQJmRgZ1LF6+cr5TPpRj6jf327AsiIq2jhYEH4oqUUkVKTor+9w2BT3oxVwhzE5lw9tcg==",
+      "version": "1.8.15",
+      "resolved": "https://registry.npmjs.org/bunyan/-/bunyan-1.8.15.tgz",
+      "integrity": "sha512-0tECWShh6wUysgucJcBAoYegf3JJoZWibxdqhTm7OHPeT42qdjkZ29QCMcKwbgU1kiH+auSIasNRXMLWXafXig==",
       "requires": {
         "dtrace-provider": "~0.8",
         "moment": "^2.19.3",
@@ -3351,7 +3351,7 @@
     "glob": {
       "version": "6.0.4",
       "resolved": "https://registry.npmjs.org/glob/-/glob-6.0.4.tgz",
-      "integrity": "sha512-MKZeRNyYZAVVVG1oZeLaWie1uweH40m9AZwIwxyPbTSX4hHrVYSzLg0Ro5Z5R7XKkIX+Cc6oD1rqeDJnwsB8/A==",
+      "integrity": "sha1-DwiGD2oVUSey+t1PnOJLGqtuTSI=",
       "optional": true,
       "requires": {
         "inflight": "^1.0.4",
@@ -4638,9 +4638,9 @@
       "integrity": "sha1-EUyUlnPiqKNenTV4hSeqN7Z52is="
     },
     "moment": {
-      "version": "2.24.0",
-      "resolved": "https://registry.npmjs.org/moment/-/moment-2.24.0.tgz",
-      "integrity": "sha512-bV7f+6l2QigeBBZSM/6yTNq4P2fNpSWj/0e7jQcy87A8e7o2nAfP/34/2ky5Vw4B9S446EtIhodAzkFCcR4dQg==",
+      "version": "2.29.1",
+      "resolved": "https://registry.npmjs.org/moment/-/moment-2.29.1.tgz",
+      "integrity": "sha512-kHmoybcPV8Sqy59DwNDY3Jefr64lK/by/da0ViFcuA4DH0vQg5Q6Ze5VimxkfQNSC+Mls/Kx53s7TjP1RhFEDQ==",
       "optional": true
     },
     "mongodb": {
@@ -4670,7 +4670,7 @@
     "mv": {
       "version": "2.1.1",
       "resolved": "https://registry.npmjs.org/mv/-/mv-2.1.1.tgz",
-      "integrity": "sha512-at/ZndSy3xEGJ8i0ygALh8ru9qy7gWW1cmkaqBN29JmMlIvM//MEO9y1sk/avxuwnPcfhkejkLsuPxH81BrkSg==",
+      "integrity": "sha1-rmzg1vbV4KT32JN5jQPB6pVZtqI=",
       "optional": true,
       "requires": {
         "mkdirp": "~0.5.1",
@@ -4692,7 +4692,7 @@
     "ncp": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/ncp/-/ncp-2.0.0.tgz",
-      "integrity": "sha512-zIdGUrPRFTUELUvr3Gmc7KZ2Sw/h1PiVM0Af/oHB6zgnV1ikqSfRk+TOufi79aHYCW3NiOXmr1BP5nWbzojLaA==",
+      "integrity": "sha1-GVoh1sRuNh0vsSgbo4uR6d9727M=",
       "optional": true
     },
     "needle": {
@@ -6288,7 +6288,7 @@
     "rimraf": {
       "version": "2.4.5",
       "resolved": "https://registry.npmjs.org/rimraf/-/rimraf-2.4.5.tgz",
-      "integrity": "sha512-J5xnxTyqaiw06JjMftq7L9ouA448dw/E7dKghkP9WpKNuwmARNNg+Gk8/u5ryb9N/Yo2+z3MCwuqFK/+qPOPfQ==",
+      "integrity": "sha1-7nEM5dk6j9uFb7Xqj/Di11k0sto=",
       "optional": true,
       "requires": {
         "glob": "^6.0.1"

services/docstore/package.json

@@ -24,6 +24,7 @@
     "@overleaf/object-persistor": "https://github.com/overleaf/object-persistor/archive/4ca62157a2beb747e9a56da3ce1569124b90378a.tar.gz",
     "async": "^2.6.3",
     "body-parser": "^1.19.0",
+    "bunyan": "^1.8.15",
     "celebrate": "^13.0.4",
     "express": "^4.17.1",
     "logger-sharelatex": "^2.2.0",
@@ -37,7 +38,6 @@
   "devDependencies": {
     "@google-cloud/storage": "^5.1.2",
     "babel-eslint": "^10.1.0",
-    "bunyan": "~1.8.14",
     "chai": "~4.2.0",
     "chai-as-promised": "^7.1.1",
     "eslint": "^6.8.0",