⬇️️ revert dependencies: knex@0.13.0 to knex@0.12.9

no issue

We have recently merged `knex:0.13.0` into Ghost master.

It was absolutely fine and it works, because yarn is smart. but...
- in case you use `npm` for the installation, the installation of the Ghost dependency fails because of a peer dependency error
- we install 2x knex, which isn't really useful
- bookshelf doesn't actually support knex 0.13.0 yet, see bookshelf/bookshelf#1566

package.json

@@ -59,7 +59,7 @@
     "intl": "1.2.5",
     "intl-messageformat": "1.3.0",
     "jsonpath": "0.2.11",
-    "knex": "0.13.0",
+    "knex": "0.12.9",
     "knex-migrator": "2.0.16",
     "lodash": "4.17.4",
     "markdown-it": "8.3.1",

yarn.lock

@@ -2876,30 +2876,7 @@ knex@0.12.2:
     tildify "~1.0.0"
     v8flags "^2.0.2"
 
-knex@0.13.0:
-  version "0.13.0"
-  resolved "https://registry.yarnpkg.com/knex/-/knex-0.13.0.tgz#08dd494f6bb64928934eec9dac34787a14ca5fa4"
-  dependencies:
-    babel-runtime "^6.11.6"
-    bluebird "^3.4.6"
-    chalk "^1.0.0"
-    commander "^2.2.0"
-    debug "^2.1.3"
-    generic-pool "^2.4.2"
-    inherits "~2.0.1"
-    interpret "^0.6.5"
-    liftoff "~2.2.0"
-    lodash "^4.6.0"
-    minimist "~1.1.0"
-    mkdirp "^0.5.0"
-    pg-connection-string "^0.1.3"
-    readable-stream "^1.1.12"
-    safe-buffer "^5.0.1"
-    tildify "~1.0.0"
-    uuid "^3.0.0"
-    v8flags "^2.0.2"
-
-knex@^0.12.8:
+knex@0.12.9, knex@^0.12.8:
   version "0.12.9"
   resolved "https://registry.yarnpkg.com/knex/-/knex-0.12.9.tgz#aa852138c09ed46181e890fd698270bbe7761124"
   dependencies:
@@ -3441,13 +3418,13 @@ mkdirp@0.3.2:
   version "0.3.2"
   resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-0.3.2.tgz#4bfb891e9c48b93d6b567f2c3cf2dd3f56bcdef8"
 
-mkdirp@0.5.0, mkdirp@^0.5.0:
+mkdirp@0.5.0:
   version "0.5.0"
   resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-0.5.0.tgz#1d73076a6df986cd9344e15e71fcc05a4c9abf12"
   dependencies:
     minimist "0.0.8"
 
-mkdirp@0.5.1, mkdirp@0.5.x, mkdirp@0.x.x, "mkdirp@>=0.5 0", mkdirp@^0.5.1, mkdirp@~0.5.0, mkdirp@~0.5.1:
+mkdirp@0.5.1, mkdirp@0.5.x, mkdirp@0.x.x, "mkdirp@>=0.5 0", mkdirp@^0.5.0, mkdirp@^0.5.1, mkdirp@~0.5.0, mkdirp@~0.5.1:
   version "0.5.1"
   resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-0.5.1.tgz#30057438eac6cf7f8c4767f38648d6697d75c903"
   dependencies: