Rebase PRs against their base branch

Put the changes on top of their base, instead of the other way around.

@@ -342,7 +342,8 @@
         { "get": "{{meta.urls.repo_api}}/pulls/{{prNum}}",             "desc": "Get the PR information", "id": "pr" },
         { "get": "{{meta.urls.repo_api}}/pulls/{{prNum}}/commits",     "desc": "Get the PR commits to access author info", "id": "prCommits" },
         [ "git checkout -b {{pr.user.login}}-{{pr.head.ref}} {{pr.base.ref}}", "Create a new branch for merging the changes" ],
-        [ "git pull --rebase {{pr.head.repo.ssh_url}} {{pr.head.ref}}",        "Merge and rebase the changes"],
+        [ "git pull {{pr.head.repo.ssh_url}}",                                 "Merge the changes"],
+        [ "git rebase {{pr.base.ref}}",                                        "Rebase against the base branch"],
         [ "git checkout {{pr.base.ref}}",                                      "Check out the base branch" ],
         { "prompt": "text", "id": "line",                              "desc": "Describe this change in one line" },
         [ "git merge --no-ff {{pr.user.login}}-{{pr.head.ref}} -m '{{line}}. Closes #{{prNum}}'", "Merge the changes" ],