Be more strict about which files are included in crate packaging

Author: lopopolo

Cargo.toml

@@ -13,7 +13,7 @@ homepage = "https://github.com/artichoke/strftime-ruby"
 description = "Ruby `Time#strftime` parser and formatter"
 keywords = ["ruby", "strftime", "time"]
 categories = ["date-and-time", "no-std", "no-std::no-alloc", "parser-implementations", "value-formatting"]
-include = ["src/**/*", "tests/**/*", "LICENSE", "README.md"]
+include = ["/src/**/*", "/tests/**/*", "/LICENSE", "/README.md"]
 
 [lib]
 name = "strftime"