Bump minor version of heapless

Cargo.toml

@@ -24,7 +24,7 @@ libc = { version = "0.2.18", optional = true }
 bitflags = { version = "1.0", default-features = false }
 defmt = { version = "0.3", optional = true }
 cfg-if = "1.0.0"
-heapless = "0.7.8"
+heapless = "0.7.15"
 
 [dev-dependencies]
 env_logger = "0.10"