Fix README.

Author: samuelsonric

README.md

@@ -18,17 +18,17 @@ using Graphs
 graph = smallgraph(:petersen)
 
 # coloring
-coloring = solve(ColoringProblem(), g)
+coloring = solve(ColoringProblem(), graph)
 coloring.colors      # coloring
 coloring.num_colors  # chromatic number
 
 # vertex cover
-cover = solve(VertexCoverProblem(), g)
+cover = solve(VertexCoverProblem(), graph)
 cover                # vertex cover
 length(cover)        # vertex cover number
 
 # dominating set
-domset = solve(DominatingSetProblem(), g)
-donset               # dominating set
+domset = solve(DominatingSetProblem(), graph)
+domset               # dominating set
 length(domset)       # domination number
 ```