Fix clippy::upper-case-acronyms

[cmichi]

Currently clippy breaks on master due to

error: name `__ink_Message_0x17FEB370` contains a capitalized acronym
  --> lib.rs:23:1
   |
23 | #[ink::contract]
   | ^^^^^^^^^^^^^^^^
   |
   = note: `-D clippy::upper-case-acronyms` implied by `-D warnings`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#upper_case_acronyms
   = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: name `__ink_Constructor_0x9BAE9D5E` contains a capitalized acronym
  --> lib.rs:23:1
   |
23 | #[ink::contract]
   | ^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#upper_case_acronyms
   = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)
error: aborting due to 2 previous errors
error: could not compile `contract_terminate`

[Robbepop]

tbh, I dislike small-letter hex-codes but this apparently is invisible to users generally anyways and causes trouble, so I approve.