update docs as per knex/knex#3416 (#233)

sections/migrations.js

@@ -158,6 +158,16 @@ export default [
       $ knex migrate:up
     `
   },
+  {
+    type: "text",
+    content: "To run the specified migration that has not yet been run"
+  },
+  {
+    type: "code",
+    content: `
+      $ knex migrate:up 001_migration_name.js
+    `
+  },
   {
     type: "text",
     content: "To undo the last migration that was run"
@@ -168,6 +178,16 @@ export default [
       $ knex migrate:down
     `
   },
+  {
+    type: "text",
+    content: "To undo the specified migration that was run"
+  },
+  {
+    type: "code",
+    content: `
+      $ knex migrate:down 001_migration_name.js
+    `
+  },
   {
     type: "text",
     content: "To list both completed and pending migrations:"
@@ -452,16 +472,16 @@ export default [
   {
     type: "method",
     method: "up",
-    example: "knex.migrate.up([config])",
+    example: "knex.migrate.up([name], [config])",
     description:
-      "Runs the next chronological migration that has not yet be run",
+      "Runs the specified or the next chronological migration that has not yet be run",
     children: []
   },
   {
     type: "method",
     method: "down",
-    example: "knex.migrate.down([config])",
-    description: "Will undo the last migration that was run",
+    example: "knex.migrate.down([name], [config])",
+    description: "Will undo the specified or the last migration that was run",
     children: []
   },
   {