[ruby/rubygems] update magnus version in rust extension gem template

ruby/rubygems@1ba8eb4ab3

Author: matsadler

lib/bundler/templates/newgem/ext/newgem/Cargo.toml.tt

@@ -12,4 +12,4 @@ publish = false
 crate-type = ["cdylib"]
 
 [dependencies]
-magnus = { version = "0.6.2" }
+magnus = { version = "0.8.2" }