bump docker version in weave-build docker image
bump docker version in weave-build docker image

to 1.3.1, the same version we use everywhere else, e.g. in weavexec.

philipz/weave,paladin74/weave,bboreham/weave,OnePaaS/weave,narry/weave,weaveworks/weave,dpw/weave,awh/weave,bboreham/weave,philipz/weave,aaam/weave,paulbellamy/weave,n054/weave,weaveworks/weave,narry/weave,awh/weave,philipz/weave,cgvarela/weave,awanke/weave,paulbellamy/weave,n054/weave,tomwilkie/weave,n054/weave,rade/weave,achanda/weave,bboreham/weave,aaam/weave,squaremo/weave,n054/weave,dpw/weave,kidaa/weave,aaam/weave,cgvarela/weave,BWITS/weave,achanda/weave,BWITS/weave,rade/weave,beni55/weave,paladin74/weave,2opremio/weave,philipz/weave,beni55/weave,aaam/weave,beni55/weave,bboreham/weave,awanke/weave,squaremo/weave,dpw/weave,awh/weave,narry/weave,narry/weave,awanke/weave,paladin74/weave,2opremio/weave,cgvarela/weave,kidaa/weave,tomwilkie/weave,weaveworks/weave,2opremio/weave,ycaihua/weave,BWITS/weave,ycaihua/weave,awanke/weave,rade/weave,philipz/weave,kidaa/weave,errordeveloper/weave,errordeveloper/weave,paladin74/weave,achanda/weave,kidaa/weave,squaremo/weave,awanke/weave,beni55/weave,beni55/weave,paulbellamy/weave,BWITS/weave,errordeveloper/weave,2opremio/weave,paulbellamy/weave,2opremio/weave,weaveworks/weave,BWITS/weave,tomwilkie/weave,achanda/weave,dpw/weave,cgvarela/weave,OnePaaS/weave,errordeveloper/weave,n054/weave,squaremo/weave,awh/weave,tomwilkie/weave,narry/weave,OnePaaS/weave,rade/weave,bboreham/weave,dpw/weave,achanda/weave,tomwilkie/weave,awh/weave,OnePaaS/weave,errordeveloper/weave,squaremo/weave,ycaihua/weave,ycaihua/weave,ycaihua/weave,cgvarela/weave,kidaa/weave,paladin74/weave,aaam/weave,OnePaaS/weave,rade/weave