Postgres character columns are not treated as string types
## Issue

### Issue description
dbt does not treat character types as string types, and therefore leaves out the length portion of the `character` column type when building columns. This happens during Archival (and likely incremental models when expanding types) on Postgres.

### Results
dbt should treat `character` as a string type, as with `varchar` and `text`.

### System information
The output of `dbt --version`:
```
0.12.x
```

### Steps to reproduce
Archive a table on Postgres with a column of type `character(36)`. dbt will recreate this column with type `character` with no size specified.


This issue was created from the description of https://github.com/fishtown-analytics/dbt/pull/1191
diff --git a/dbt/schema.py b/dbt/schema.py
index 3a34903a8..f4b75e7b6 100644
--- a/dbt/schema.py
+++ b/dbt/schema.py
@@ -45,7 +45,7 @@ class Column(object):
             return self.dtype
 
     def is_string(self):
-        return self.dtype.lower() in ['text', 'character varying']
+        return self.dtype.lower() in ['text', 'character varying', 'character']
 
     def is_numeric(self):
         return self.dtype.lower() in ['numeric', 'number']
diff --git a/test/unit/test_schema.py b/test/unit/test_schema.py
index a7c3d94ff..6c065a422 100644
--- a/test/unit/test_schema.py
+++ b/test/unit/test_schema.py
@@ -2,6 +2,17 @@ import unittest
 
 import dbt.schema
 
+class TestStringType(unittest.TestCase):
+
+    def test__character_type(self):
+        col = dbt.schema.Column(
+            'fieldname',
+            'character',
+            char_size=10
+        )
+
+        self.assertEqual(col.data_type, 'character varying(10)')
+
 
 class TestNumericType(unittest.TestCase):
 
['dbt/schema.py', 'test/unit/test_schema.py']