upgrade lru dependency to 0.7.8 (#15)

This fixes this vulnerability GHSA-v362-2895-h9r2

Author: uwemaurer

Cargo.toml

@@ -17,12 +17,12 @@ futures = "0.3.14"
 thiserror = "1.0"
 
 # Optional feature based dependencies
-lru = { version = "0.6.5", optional = true }
+lru = { version = "0.7.8", optional = true }
 
 [dev-dependencies]
 cache_loader_async_macros = { path = "./cache-loader-async-macros" }
 
 [features]
 default = []
 lru-cache = ["lru"]
-ttl-cache = []
+ttl-cache = []