DOC: create 1.12 docs from a tag like v1.12.2rc1 (#71985)

Summary:
brianjo, malfet

The documentation team would prefer the [documentation versions] to only have a major.minor version, not major.minor.patch. See also pytorch/pytorch.github.io#921

The regex can be tested by this bash 1-liner (where $tag is something like `v10.1225.0rc1`)
```
echo $tag | sed -e 's/v*\([0-9]*\.[0-9]*\).*/\1/'
```

I have lost track a bit, is the CI run for a tag actually building and pushing documentation?

Pull Request resolved: pytorch/pytorch#71985

Reviewed By: mrshenli

Differential Revision: D33845882

Pulled By: malfet

fbshipit-source-id: 3cb644d8b01f5ddf87c0ac7c43e23e9fd292d660
(cherry picked from commit f884bd8)

Author: mattip

.circleci/config.yml

@@ -43,8 +43,8 @@
           set -ex
           export COMMIT_DOCKER_IMAGE=${DOCKER_IMAGE}:build-${DOCKER_TAG}-${CIRCLE_SHA1}
           echo "DOCKER_IMAGE: "${COMMIT_DOCKER_IMAGE}
-          # turn v1.12.0rc3 into 1.12.0
-          tag=$(echo $CIRCLE_TAG | sed -e 's/v*\([0-9.]*\).*/\1/')
+          # turn v1.12.0rc3 into 1.12
+          tag=$(echo $CIRCLE_TAG | sed -e 's/v*\([0-9]*\.[0-9]*\).*/\1/')
           target=${tag:-master}
           echo "building for ${target}"
           time docker pull ${COMMIT_DOCKER_IMAGE} >/dev/null
@@ -89,9 +89,8 @@
           set -ex
           export COMMIT_DOCKER_IMAGE=${DOCKER_IMAGE}:build-${DOCKER_TAG}-${CIRCLE_SHA1}
           echo "DOCKER_IMAGE: "${COMMIT_DOCKER_IMAGE}
-          # turn v1.12.0rc3 into 1.12.0
-          tag=$(echo $CIRCLE_TAG | sed -e 's/v*\([0-9.]*\).*/\1/')
-          tag=${CIRCLE_TAG:1:5}
+          # turn v1.12.0rc3 into 1.12
+          tag=$(echo $CIRCLE_TAG | sed -e 's/v*\([0-9]*\.[0-9]*\).*/\1/')
           target=${tag:-master}
           echo "building for ${target}"
           time docker pull ${COMMIT_DOCKER_IMAGE} >/dev/null