Fix issues with the linux package builds and the README

This is just a collection of short-term fixes:
- pin the latest .msi package in the README, instead of using a specific version
- use `go get -d` for the go-bin-deb and go-bin-rpm packages, to only download the source (without building them) before we use glide to get their precise dependencies
- inject the new full version information in the build process

As mentioned in #1247 (comment), we should build and test the linux packages regularly, so we can fix them if something breaks...

Author: na--

.circleci/config.yml

@@ -123,13 +123,13 @@ jobs:
             export PATH=$GOPATH/bin:$PATH
 
             go get github.com/Masterminds/glide
-            go get github.com/mh-cbon/go-bin-deb \
+            go get -d github.com/mh-cbon/go-bin-deb \
               && cd $GOPATH/src/github.com/mh-cbon/go-bin-deb \
               && glide install \
               && go install
 
-            go get github.com/mh-cbon/go-bin-rpm \
-              && cd $GOPATHsrc/github.com/mh-cbon/go-bin-rpm \
+            go get -d github.com/mh-cbon/go-bin-rpm \
+              && cd $GOPATH/src/github.com/mh-cbon/go-bin-rpm \
               && glide install \
               && go install
 
@@ -139,7 +139,7 @@ jobs:
             cd $GOPATH/src/github.com/loadimpact/k6
 
             echo "Building k6..."
-            CGO_ENABLED=0 GOARCH=$ARCH go build -a -trimpath -ldflags '-s -w' -o /tmp/k6
+            CGO_ENABLED=0 GOARCH=amd64 go build -a -trimpath -ldflags "-s -w -X github.com/loadimpact/k6/lib/consts.VersionDetails=$(date -u +"%FT%T%z")/$(git describe --always --long --dirty)" -o /tmp/k6
             echo "Done!"
 
             VERSION=${CIRCLE_TAG:1} ./packaging/gen-packages.sh

README.md

@@ -66,7 +66,7 @@ brew install k6
 
 ### Windows
 
-You can manually download and install the [official `.msi` installation package](https://dl.bintray.com/loadimpact/windows/k6-v0.25.1-amd64.msi) or, if you use the [chocolatey package manager](https://chocolatey.org/), follow [these instructions](https://bintray.com/repo/buildSettings?repoPath=%2Floadimpact%2Fchoco) to set up the k6 repository.
+You can manually download and install the [official `.msi` installation package](https://dl.bintray.com/loadimpact/windows/k6-latest-amd64.msi) or, if you use the [chocolatey package manager](https://chocolatey.org/), follow [these instructions](https://bintray.com/repo/buildSettings?repoPath=%2Floadimpact%2Fchoco) to set up the k6 repository.
 
 ### Linux