fix doctests

Author: hyrodium

src/priorityqueue.jl

@@ -144,7 +144,7 @@ Verify if priority queue `pq` has `key` in its keys.
 # Example
 
 ```jldoctest
-ulia> pq = PriorityQueue("a" => 1, "b" => 2, "c" => 3)
+julia> pq = PriorityQueue("a" => 1, "b" => 2, "c" => 3)
 PriorityQueue{String, Int64, Base.Order.ForwardOrdering} with 3 entries:
   "a" => 1
   "b" => 2

src/stack.jl

@@ -93,7 +93,7 @@ julia> for i in range(1, 0.2, 5)
 julia> s
 Stack{Float32}(Deque [Float32[1.0, 0.8, 0.6, 0.4, 0.2]])
 
-julia> first(s)
+julia> last(s)
 1.0f0
 ```
 """