chore: update the target compiler version to nightly-2020-07-07

`const_if_match` and `const_loop` have been stabilized by
<rust-lang/rust#72437>.

examples/basic/src/main.rs

@@ -1,6 +1,4 @@
-#![feature(const_loop)]
 #![feature(const_fn)]
-#![feature(const_if_match)]
 #![feature(const_mut_refs)]
 #![feature(unsafe_block_in_unsafe_fn)] // `unsafe fn` doesn't imply `unsafe {}`
 #![deny(unsafe_op_in_unsafe_fn)]

rust-toolchain

@@ -1 +1 @@
-nightly-2020-06-24
+nightly-2020-07-07

src/constance/src/lib.rs

@@ -1,8 +1,6 @@
 #![feature(external_doc)] // `#[doc(include = ...)]`
 #![feature(const_fn)]
-#![feature(const_if_match)]
 #![feature(const_panic)]
-#![feature(const_loop)]
 #![feature(const_generics)]
 #![feature(const_ptr_offset)]
 #![feature(const_mut_refs)]

src/constance_port_std/tests/test_suite.rs

@@ -1,6 +1,4 @@
 //! Runs test cases defined in `constance_test_suite`.
-#![feature(const_loop)]
-#![feature(const_if_match)]
 #![feature(never_type)]
 #![feature(const_mut_refs)]
 #![feature(const_fn)]

src/constance_test_suite/src/lib.rs

@@ -1,7 +1,5 @@
 #![feature(external_doc)] // `#[doc(include = ...)]`
-#![feature(const_loop)]
 #![feature(const_fn)]
-#![feature(const_if_match)]
 #![feature(unsafe_block_in_unsafe_fn)] // `unsafe fn` doesn't imply `unsafe {}`
 #![deny(unsafe_op_in_unsafe_fn)]
 #![doc(include = "./lib.md")]