Add description capitalization rule

Signed-off-by: Chris Potter <chris@reactioncommerce.com>

.reaction/graphql-linter/rules/description_fields_capitalized.js

@@ -0,0 +1,33 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.DescriptionsAreCapitalized = DescriptionsAreCapitalized;
+
+var _validation_error = require("graphql-schema-linter/lib/validation_error");
+var schema = require('graphql/utilities/buildASTSchema');
+
+function DescriptionsAreCapitalized(configuration, context) {
+  return {
+    FieldDefinition(node, key, parent, path, ancestors) {
+      var description = schema.getDescription(node, {
+        commentDescriptions: configuration.getCommentDescriptions(),
+      })
+      if (description && description[0] === description[0].toUpperCase()) {
+        return;
+      }
+
+      const fieldName = node.name.value;
+      const parentName = ancestors[ancestors.length - 1].name.value;
+
+      context.reportError(
+        new _validation_error.ValidationError(
+          'descriptions-are-capitalized',
+          `The description for field \`${parentName}.${fieldName}\` should be capitalized.`,
+          [node]
+        )
+      );
+    },
+  };
+}

package.json

@@ -439,7 +439,8 @@
       "relay-page-info-spec",
       "type-fields-sorted-alphabetically",
       "types-are-capitalized",
-      "types-have-descriptions"
+      "types-have-descriptions",
+      "descriptions-are-capitalized"
     ]
   }
 }