Add missing target for bash_completion task.

Pushed TBR to fix build.

Testing Done:
CI passes: https://travis-ci.org/pantsbuild/pants/builds/65578880

Bugs closed: 1642

Reviewed at https://rbcommons.com/s/twitter/r/2326/

src/python/pants/backend/core/tasks/BUILD

@@ -4,6 +4,7 @@
 target(
   name = 'all',
   dependencies = [
+    ':bash_completion',
     ':builddictionary',
     ':changed_target_goals',
     ':clean',
@@ -42,6 +43,18 @@ target(
   ]
 )
 
+python_library(
+  name = 'bash_completion',
+  sources = ['bash_completion.py'],
+  dependencies = [
+    ':console_task',
+    'src/python/pants/base:exceptions',
+    'src/python/pants/base:generator',
+    'src/python/pants/goal',
+    'src/python/pants/option',
+    ],
+  )
+
 python_library(
   name = 'builddictionary',
   sources = ['builddictionary.py'],

src/python/pants/backend/core/tasks/bash_completion.py

@@ -13,7 +13,7 @@
 
 from pants.backend.core.tasks.console_task import ConsoleTask
 from pants.base.exceptions import TaskError
-from pants.base.generator import Generator, TemplateData
+from pants.base.generator import Generator
 from pants.goal.goal import Goal
 from pants.option.arg_splitter import GLOBAL_SCOPE