Use OCaml 4.09 for Travis CI

[XVilka]

Apparently there are no dependencies that restrict the most modern OCaml version use.

[XVilka]

Aha, error because of the camlp5 deprecation:

coq_makefile -f Make -o CoqMakefile
camlp5 macro files not supported anymore, please port src/commands.ml4 to coqpp
Usage summary:

coq_makefile .... [file.v] ... [file.ml[i4]?] ... [file.ml{lib,pack}]
  ... [any] ... [-extra[-phony] result dependencies command]
  ... [-I dir] ... [-R physicalpath logicalpath]
  ... [-Q physicalpath logicalpath] ... [VARIABLE = value]
  ...  [-arg opt] ... [-opt|-byte] [-no-install] [-f file] [-o file]
  [-h] [--help]

Full list of options:

[file.v]: Coq file to be compiled
[file.ml[i4]?]: Objective Caml file to be compiled
[file.ml{lib,pack}]: ocamlbuild-style file that describes a Objective Caml
  library/module
[any] : subdirectory that should be "made" and has a Makefile itself
  to do so. Very fragile and discouraged.
[-extra result dependencies command]: add target "result" with command
  "command" and dependencies "dependencies". If "result" is not
  generic (do not contains a %), "result" is built by _make all_ and
  deleted by _make clean_.
[-extra-phony result dependencies command]: add a PHONY target "result"
 with command "command" and dependencies "dependencies". Note that
 _-extra-phony foo bar ""_ is a regular way to add the target "bar" as
 as a dependencies of an already defined target "foo".
[-I dir]: look for Objective Caml dependencies in "dir"
[-R physicalpath logicalpath]: look for Coq dependencies recursively
  starting from "physicalpath". The logical path associated to the
  physical path is "logicalpath".
[-Q physicalpath logicalpath]: look for Coq dependencies starting from
  "physicalpath". The logical path associated to the physical path
  is "logicalpath".
[VARIABLE = value]: Add the variable definition "VARIABLE=value"
[-byte]: compile with byte-code version of coq
[-opt]: compile with native-code version of coq
[-arg opt]: send option "opt" to coqc
[-install opt]: where opt is "user" to force install into user directory,
  "none" to build a makefile with no install target or
  "global" to force install in $COQLIB directory
[-f file]: take the contents of file as arguments
[-o file]: output should go in file file (recommended)
	Output file outside the current directory is forbidden.
[-h]: print this usage summary
[--help]: equivalent to [-h]
make: *** [CoqMakefile] Error 1