use ^ for more dependencies in pubspec.yaml

pubspec.yaml

@@ -22,10 +22,10 @@ executables:
 
 dependencies:
   args: '>=0.12.0+1 <0.14.0'
-  crypto: '>=0.9.0 <0.10.0'
-  http: '>=0.11.0 <0.12.0'
-  path: '>=1.3.0 <2.0.0'
-  usage: '>=1.0.0 <2.0.0'
+  crypto: ^0.9.0
+  http: ^0.11.0
+  path: ^1.3.0
+  usage: ^1.0.0
 
 dev_dependencies:
   browser: ^0.10.0