Fix markdown in source_maps README.md so it renders correctly in pub site.

pkg/source_maps/README.md

Index: pkg/source_maps/README.md
diff --git a/pkg/source_maps/README.md b/pkg/source_maps/README.md
index df182d9ba77c903a044e2f4ed45610ef7cf12f45..5c7f638f40c825b215ad3a010651579514370cb5 100644
--- a/pkg/source_maps/README.md
+++ b/pkg/source_maps/README.md
@@ -7,6 +7,7 @@ originated from the [Closure Compiler][closure] and has been implemented in
 Chrome and Firefox.
 
 In this package we provide:
+
   * Data types defining file locations and spans: these are not part of the
     original source map specification. These data types are great for tracking
     source locations on source maps, but they can also be used by tools to
@@ -17,6 +18,7 @@ In this package we provide:
     mapping information.
 
 Some upcoming features we are planning to add to this package are:
+
   * A printer that lets you generate code, but record source map information in
     the process.
   * A tool that can compose source maps together. This would be useful for