Update BOSH to 266.3.0 and bump stemcell to 3586.24

We have encountered an issue [1] of a process putting a VM under load that causes
monit to drop the connections. This is fixed in the 266.x series, therefore we
should upgrade to that.

We bump the stemcell to the latest versions because:
* we want to have the latest security updates
* the precompiled BOSH release is only created for the latest stemcell versions

[1] cloudfoundry/bosh#1754

manifests/bosh-manifest/bosh-manifest.yml

@@ -20,9 +20,9 @@ meta:
 
 releases:
 - name: bosh
-  version: "265.2.0"
-  url: https://s3.amazonaws.com/bosh-compiled-release-tarballs/bosh-265.2.0-ubuntu-trusty-3541.25-20180510-015838-907353893-20180510015842.tgz?versionId=6Ym0RSiSuRalyo5kFG40Zt.dnwcR28G3
-  sha1: e40aebe0018a69964f2e9a3b93e6a6e79705c581
+  version: "266.3.0"
+  url: https://s3.amazonaws.com/bosh-compiled-release-tarballs/bosh-266.3.0-ubuntu-trusty-3586.24-20180618-222058-780666232-20180618222102.tgz?versionId=ZimzyeHk7GP9tPp4m.X25HOe35yPgj9F
+  sha1: acf356e49dd5310fe7733b6fc059f6d31afb2729
 - name: bosh-aws-cpi
   version: 69
   url: https://bosh.io/d/github.com/cloudfoundry-incubator/bosh-aws-cpi-release?v=69
@@ -172,8 +172,8 @@ resource_pools:
 - name: bosh
   network: private
   stemcell:
-    url: https://bosh.io/d/stemcells/bosh-aws-xen-hvm-ubuntu-trusty-go_agent?v=3541.25
-    sha1: 8607e8ccd8a66dc0248535f1d66d5b45d7a4db1d
+    url: https://bosh.io/d/stemcells/bosh-aws-xen-hvm-ubuntu-trusty-go_agent?v=3586.24
+    sha1: dced51326eaa156cf634ff795631e4358d795385
   cloud_properties:
     instance_type: t2.medium
     ephemeral_disk: {size: 40000, type: gp2}