snap: release non-stable-semver tags to beta (#3865)

* snap: release non-stable-semver tags to beta

- fixes #3860

* snap: document --beta

Author: casperdcl

README.rst

@@ -101,7 +101,8 @@ Snap (Snapcraft/Linux)
    snap install dvc --classic
 
 This corresponds to the latest tagged release.
-Add ``--edge`` for the latest ``master`` version.
+Add ``--beta`` for the latest tagged release candidate,
+or ``--edge`` for the latest ``master`` version.
 
 Choco (Chocolatey/Windows)
 --------------------------

scripts/ci/before_install.sh

@@ -52,7 +52,11 @@ elif [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
 fi
 
 if [[ -n "$TRAVIS_TAG" ]]; then
-  echo "export SNAP_CHANNEL=stable" >>env.sh
+  if [[ $(echo "$TRAVIS_TAG" | grep -E '^[0-9]+\.[0-9]+\.[0-9]+$') ]]; then
+    echo "export SNAP_CHANNEL=stable" >>env.sh
+  else
+    echo "export SNAP_CHANNEL=beta" >>env.sh
+  fi
 else
   echo "export SNAP_CHANNEL=edge" >>env.sh
 fi