make link more pleasant to eye (rust-lang#1777)

Author: tshepang

src/llvm-coverage-instrumentation.md

@@ -84,7 +84,7 @@ the Rust source code.
 
 Note that many of these `Coverage` statements will _not_ be converted into
 physical counters (or any other executable instructions) in the final binary.
-Some of them will be (see `CoverageKind::`[`Counter`][counter-coverage-kind]),
+Some of them will be (see [`CoverageKind::Counter`]),
 but other counters can be computed on the fly, when generating a coverage
 report, by mapping a `CodeRegion` to a
 `CoverageKind`::[`Expression`][expression-coverage-kind].
@@ -131,7 +131,7 @@ The `InstrumentCoverage` MIR pass is documented in
 [mir-passes]: mir/passes.md
 [mir-instrument-coverage]: https://github.com/rust-lang/rust/tree/master/compiler/rustc_mir_transform/src/coverage
 [code-region]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/coverage/struct.CodeRegion.html
-[counter-coverage-kind]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/coverage/enum.CoverageKind.html#variant.Counter
+[`CoverageKind::Counter`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/coverage/enum.CoverageKind.html#variant.Counter
 [expression-coverage-kind]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/coverage/enum.CoverageKind.html#variant.Expression
 [coverage-statement]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/enum.StatementKind.html#variant.Coverage
 [instrument-coverage-pass-details]: #implementation-details-of-the-instrumentcoverage-mir-pass