Change from concat to into, to ensure vector

Since pomegranate mentions that it likes vectors as inputs to its
functions, this commit changes the normalization function to use
`into` instead of `concat`, to make sure that we get a vector instead
of a sequence.

leiningen-core/src/leiningen/core/classpath.clj

@@ -548,7 +548,7 @@
       ;; it's important to preserve the metadata, because it is used for
       ;; profile merging, etc.
       (with-meta
-       (concat [id version] opts)
+       (into [id version] opts)
        (meta dep)))))
 
 (defn normalize-dep-vectors