Dart fix and fix warnings.

analysis_options.yaml

diff --git a/analysis_options.yaml b/analysis_options.yaml
index f7b8674..0d2bc74 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -12,9 +12,9 @@
 # https://github.com/dart-lang/sdk/tree/master/pkg/analyzer#configuring-the-analyzer
 
 analyzer:
-  strong-mode:
-    implicit-casts: false
-    implicit-dynamic: false
+  language:
+    strict-casts: false
+    strict-raw-types: false
   errors:
     # treat missing required parameters as a warning (not a hint)
     missing_required_param: warning
@@ -38,7 +38,6 @@
     - always_declare_return_types
     - always_put_control_body_on_new_line
     # - always_put_required_named_parameters_first # we prefer having parameters in the same order as fields https://github.com/flutter/flutter/issues/10219
-    - always_require_non_null_named_parameters
     - always_specify_types
     # - always_use_package_imports # we do this commonly
     - annotate_overrides
@@ -143,7 +142,6 @@
     # - prefer_constructors_over_static_methods # far too many false positives
     - prefer_contains
     # - prefer_double_quotes # opposite of prefer_single_quotes
-    - prefer_equal_for_default_values
     # - prefer_expression_function_bodies # conflicts with https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#consider-using--for-short-functions-and-methods
     - prefer_final_fields
     - prefer_final_in_for_each

lib/src/process_runner.dart

diff --git a/lib/src/process_runner.dart b/lib/src/process_runner.dart
index 16b44fe..277eac0 100644
--- a/lib/src/process_runner.dart
+++ b/lib/src/process_runner.dart
@@ -264,11 +264,11 @@
       }
     } on ProcessException catch (e) {
       final String message = 'Running "${commandLine.join(' ')}" in ${workingDirectory.path} '
-          'failed with:\n${e.toString()}';
+          'failed with:\n$e';
       throw ProcessRunnerException(message);
     } on ArgumentError catch (e) {
       final String message = 'Running "${commandLine.join(' ')}" in ${workingDirectory.path} '
-          'failed with:\n${e.toString()}';
+          'failed with:\n$e';
       throw ProcessRunnerException(message);
     }