Fix PSKModem and update gitignore

Author: Ravi Sharan

.gitignore

@@ -5,4 +5,6 @@
 
 /doc/_build
 /doc/generated
-
+/build
+/dist
+/scikit_commpy.egg-info

commpy/modulation.py

@@ -112,8 +112,8 @@ def __init__(self, m):
         self.m = m
         self.num_bits_symbol = int(log2(self.m))
         self.symbol_mapping = arange(self.m)
-        self.constellation = map(self._constellation_symbol,
-                                 self.symbol_mapping)
+        self.constellation = array(map(self._constellation_symbol,
+                                 self.symbol_mapping))
 
 class QAMModem(Modem):
     """ Creates a Quadrature Amplitude Modulation (QAM) Modem object."""