strip spaces on Add Repository because some copy/pastes would fail


copy pasting this link:
` https://sublime.wbond.net/alpha/packages.json `
from this page: http://wbond.net/sublime_packages/package_control/installation#ST3
which is right below this text: `Run the Package Control: Add Repository command via the command palette and enter the following URL:` on that page
causes the Add Repository to fail because apparently the paste made it have a leading and trailing space

tested in sublimetext3