Use :read-file-form instead of :read-file-line to work on SBCL.

SBCL still uses asdf version 3.0.2. It appears that in this version of ASDF, :read-file-line does not work correctly, incorrectly passing an :at parameter to uiop/stream:call-with-input-stream, which causes an error. :read-file-form does not have this problem.