update coverage

Coverage update was caused by upgrading to Rust 1.52.1.

Since this is a significant change in coverage, I took a look at the
difference in the coverage report from the previous Rust version and
this one.

Previously, kcov reported 3192 instrumented lines, and 1780 executed
lines.
With the new version, kcov reports 2608 instrumented lines, and 1781
executed lines.

Looking at the coverage report I can't notice anything fishy.

Signed-off-by: Andreea Florescu <fandree@amazon.com>

Author: andreeaflorescu

coverage_config_x86_64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 55.8,
+  "coverage_score": 68.3,
   "exclude_path": "",
   "crate_features": "fam-wrappers"
 }