build: update build_runner

CHANGELOG.md

@@ -1,3 +1,7 @@
-## 0.0.1
+## 0.1.1
 
-* TODO: Describe initial release.
+- doc & build updates
+
+## 0.1.0
+
+- Initial release

build.yaml

@@ -1,6 +1,6 @@
 builders:
   bin_builder:
-    import: 'tools/bin_builder.dart'
+    import: 'tool/bin_builder.dart'
     builder_factories: ['binBuilder']
     build_extensions: { '.bin.dart': ['.dart'] }
     build_to: source

pubspec.yaml

@@ -7,7 +7,7 @@ executables:
   btool: btool
 
 environment:
-  sdk: '>=2.19.0-255.2.beta <3.0.0'
+  sdk: '>=2.18.0 <3.0.0'
 
 dependencies:
   args: ^2.3.1