Fix typo in panic() message (extra single quote) (#1352)

Also fix the same typo in a comment

tree.go

@@ -232,7 +232,7 @@ func (n *node) addRoute(path string, handlers HandlersChain) {
 
 			} else if i == len(path) { // Make node a (in-path) leaf
 				if n.handlers != nil {
-					panic("handlers are already registered for path ''" + fullPath + "'")
+					panic("handlers are already registered for path '" + fullPath + "'")
 				}
 				n.handlers = handlers
 			}
@@ -247,7 +247,7 @@ func (n *node) addRoute(path string, handlers HandlersChain) {
 func (n *node) insertChild(numParams uint8, path string, fullPath string, handlers HandlersChain) {
 	var offset int // already handled bytes of the path
 
-	// find prefix until first wildcard (beginning with ':'' or '*'')
+	// find prefix until first wildcard (beginning with ':' or '*')
 	for i, max := 0, len(path); numParams > 0; i++ {
 		c := path[i]
 		if c != ':' && c != '*' {