Roll Observatory packages and add a roll script

packages/watcher/CHANGELOG.md

Index: packages/watcher/CHANGELOG.md
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+# 0.9.7
+
+* Fix a bug in `FileWatcher` where events could be added after watchers were
+  closed.
+
+# 0.9.6
+
+* Add a `Watcher` interface that encompasses watching both files and
+  directories.
+
+* Add `FileWatcher` and `PollingFileWatcher` classes for watching changes to
+  individual files.
+
+* Deprecate `DirectoryWatcher.directory`. Use `DirectoryWatcher.path` instead.
+
+# 0.9.5
+
+* Fix bugs where events could be added after watchers were closed.
+
+# 0.9.4
+
+* Treat add events for known files as modifications instead of discarding them
+  on Mac OS.
+
+# 0.9.3
+
+* Improved support for Windows via `WindowsDirectoryWatcher`.
+
+* Simplified `PollingDirectoryWatcher`.
+
+* Fixed bugs in `MacOSDirectoryWatcher`