usa missing AZ (Arizona) as neighbor to NM (new mexico) (#977)

`usa` in csp.py incorrectly has NM not being a neighbor with AZ.

Author: kjacks21

csp.py

@@ -451,7 +451,7 @@ def parse_neighbors(neighbors, variables=None):
 
 usa = MapColoringCSP(list('RGBY'),
                      """WA: OR ID; OR: ID NV CA; CA: NV AZ; NV: ID UT AZ; ID: MT WY UT;
-        UT: WY CO AZ; MT: ND SD WY; WY: SD NE CO; CO: NE KA OK NM; NM: OK TX;
+        UT: WY CO AZ; MT: ND SD WY; WY: SD NE CO; CO: NE KA OK NM; NM: OK TX AZ;
         ND: MN SD; SD: MN IA NE; NE: IA MO KA; KA: MO OK; OK: MO AR TX;
         TX: AR LA; MN: WI IA; IA: WI IL MO; MO: IL KY TN AR; AR: MS TN LA;
         LA: MS; WI: MI IL; IL: IN KY; IN: OH KY; MS: TN AL; AL: TN GA FL;