Should not read backup or temporary files under hash/

[na4zagin3]

@gfngfn reported that satyrographos install failed due to backup file mathfonts.satysfi-hash~ created by Emacs. https://satysfi.slack.com/archives/CSKJZMV33/p1583062329006600

% satyrographos install
Reading runtime dist: /usr/local/share/satysfi/dist
Uncaught exception:
  Yojson.Json_error("Line 3, bytes 5-37:\nExpected ',' or '}' but found '(\"lmodern\", append_directory \"lat'")
Raised at file "common.ml", line 5, characters 19-39
Called from file "lib/read.mll", line 286, characters 23-47
Called from file "lib/read.ml" (inlined), line 1065, characters 3-39
Called from file "lib/read.mll", line 1162, characters 8-26
Called from file "lib/read.mll", line 1183, characters 6-26
Called from file "lib/read.mll", line 1190, characters 14-47
Re-raised at file "lib/read.mll", line 1195, characters 6-13
Called from file "src/library.ml", line 144, characters 13-33
Called from file "src/FileUtilFIND.ml", line 78, characters 8-20
Called from file "array.ml", line 158, characters 9-30
Called from file "array.ml", line 158, characters 9-30
Called from file "src/commandInstall.ml", line 77, characters 21-54
Called from file "src/commandInstall.ml", line 197, characters 20-66
Called from file "src/command.ml", line 2817, characters 8-205
Called from file "src/exn.ml", line 107, characters 6-10

To prevent such a failure, Satyrographos needs to ignore files whose extensions are other than .satysfi-hash.