jingoo 1.2.16-1.2.19 are not compatible with ocaml-5
Use String.uppercase
```
=== ERROR while compiling jingoo.1.2.18 ======================================#
context 2.2.0~alpha~dev | linux/x86_64 | ocaml-base-compiler.5.0.0 | file:///home/opam/opam-repository
path ~/.opam/5.0/.opam-switch/build/jingoo.1.2.18
command ~/.opam/opam-init/hooks/sandbox.sh build make
exit-code 2
env-file ~/.opam/log/jingoo-7-326b08.env
output-file ~/.opam/log/jingoo-7-326b08.out
make -C src
make[1]: Entering directory '/home/opam/.opam/5.0/.opam-switch/build/jingoo.1.2.18/src'
ocamlyacc jg_parser.mly
1 rule never reduced
230 shift/reduce conflicts, 121 reduce/reduce conflicts.
ocamllex jg_lexer.mll
230 states, 11598 transitions, table size 47772 bytes
ocamlfind ocamlc -g -package unix,dynlink,pcre,uutf -c jg_types.mli jg_types.ml jg_utils.ml jg_stub.mli jg_stub.ml jg_parser.mli jg_parser.ml jg_lexer.ml jg_runtime.ml jg_interp.ml jg_template.mli jg_template.ml
File "jg_runtime.ml", line 281, characters 16-32:
281 | | _ -> (try Jg_stub.get_func obj_name prop_name with Not_found -> Tnull)
^^^^^^^^^^^^^^^^
Warning 6 [labels-omitted]: labels namespace, func_name were omitted in the application of this function.
File "jg_runtime.ml", line 598, characters 24-40:
598 | | Tstr str -> Tstr (String.uppercase str)
^^^^^^^^^^^^^^^^
Error: Unbound value String.uppercase
make[1]: *** [Makefile:36: jingoo.cma] Error 2
make[1]: Leaving directory '/home/opam/.opam/5.0/.opam-switch/build/jingoo.1.2.18/src'
make: *** [Makefile:0: all] Error 2
```
Signed-off-by: Marcello Seri <marcello.seri@gmail.com>