Fix button group class

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "bootstrap-rs"
-version = "0.2.1"
+version = "0.2.2"
 authors = ["Thomas Gideon <cmdln@thecommandline.net>"]
 edition = "2018"
 

src/button/mod.rs

@@ -37,7 +37,7 @@ impl Component for ButtonGroup {
 impl ButtonGroup {
     fn class(&self) -> String {
         if self.props.class.is_empty() {
-            "btn-grp".into()
+            "btn-group".into()
         } else {
             format!("btn-group {}", self.props.class)
         }