Fix small typos (#717)

* Fix typos

* Fix typo

* Fix typo

tensorpack/contrib/keras.py

@@ -78,7 +78,7 @@ class KerasPhaseCallback(Callback):
         self._learning_phase = keras.backend.learning_phase()
 
     def _setup_graph(self):
-        logger.info("Using Keras leraning phase {} in the graph!".format(
+        logger.info("Using Keras learning phase {} in the graph!".format(
             self._learning_phase.name))
         cbs = self.trainer._callbacks.cbs
         for cb in cbs:

tensorpack/graph_builder/distributed.py

@@ -267,7 +267,7 @@ class DistributedReplicatedBuilder(DataParallelBuilder, DistributedBuilderBase):
             1. the training op.
 
             2. the op which sync all the local variables from PS.
-            This op sholud be run before training.
+            This op should be run before training.
 
             3. the op which sync all the local `MODEL_VARIABLES` from PS.
             You can choose how often to run it by yourself.

tensorpack/graph_builder/model_desc.py

@@ -105,7 +105,7 @@ class ModelDescBase(object):
             with tf.Graph().as_default() as G:   # create these placeholder in a temporary graph
                 inputs = self.inputs()
                 for p in inputs:
-                    assert p.graph == G, "Placeholders returned by inputs() sholud be created inside inputs()!"
+                    assert p.graph == G, "Placeholders returned by inputs() should be created inside inputs()!"
                 return [InputDesc.from_placeholder(p) for p in inputs]
 
     def _get_inputs(self):