[eacsl] Update copyright year to 2021

src/plugins/e-acsl/src/analyses/memory_tracking.ml

src/plugins/e-acsl/src/analyses/memory_tracking.mli

src/plugins/e-acsl/src/analyses/rte.ml

src/plugins/e-acsl/src/analyses/rte.mli

src/plugins/e-acsl/src/analyses/typing.ml

src/plugins/e-acsl/src/analyses/typing.mli

src/plugins/e-acsl/src/code_generator/assert.ml

src/plugins/e-acsl/src/code_generator/assert.mli

src/plugins/e-acsl/src/code_generator/assigns.ml

src/plugins/e-acsl/src/code_generator/assigns.mli

src/plugins/e-acsl/src/code_generator/at_with_lscope.ml

src/plugins/e-acsl/src/code_generator/at_with_lscope.mli

src/plugins/e-acsl/src/code_generator/contract.ml

src/plugins/e-acsl/src/code_generator/contract.mli

src/plugins/e-acsl/src/code_generator/contract_types.mli

src/plugins/e-acsl/src/code_generator/env.ml

src/plugins/e-acsl/src/code_generator/env.mli

src/plugins/e-acsl/src/code_generator/global_observer.ml

src/plugins/e-acsl/src/code_generator/global_observer.mli

src/plugins/e-acsl/src/code_generator/gmp.ml