Remove void return type from setters (#71)

Remove void return type from setters to be compliant
with the [avoid_return_types_on_setters] lint
diff --git a/lib/message_generator.dart b/lib/message_generator.dart
index 9531dbc..a135eff 100644
--- a/lib/message_generator.dart
+++ b/lib/message_generator.dart
@@ -336,12 +336,12 @@
         var fastSetter = field.baseType.setter;
         _emitOverrideIf(field.overridesSetter, out);
         if (fastSetter != null) {
-          out.println('void set ${names.fieldName}'
+          out.println('set ${names.fieldName}'
               '($fieldTypeString v) { '
               '$fastSetter(${field.index}, ${field.number}, v);'
               ' }');
         } else {
-          out.println('void set ${names.fieldName}'
+          out.println('set ${names.fieldName}'
               '($fieldTypeString v) { '
               'setField(${field.number}, v);'
               ' }');
diff --git a/test/file_generator_test.dart b/test/file_generator_test.dart
index 50eb849..7d54352 100644
--- a/test/file_generator_test.dart
+++ b/test/file_generator_test.dart
@@ -106,17 +106,17 @@
   }
 
   String get number => $_get(0, 1, '');
-  void set number(String v) { $_setString(0, 1, v); }
+  set number(String v) { $_setString(0, 1, v); }
   bool hasNumber() => $_has(0, 1);
   void clearNumber() => clearField(1);
 
   int get type => $_get(1, 2, 0);
-  void set type(int v) { $_setUnsignedInt32(1, 2, v); }
+  set type(int v) { $_setUnsignedInt32(1, 2, v); }
   bool hasType() => $_has(1, 2);
   void clearType() => clearField(2);
 
   String get name => $_get(2, 3, '\$');
-  void set name(String v) { $_setString(2, 3, v); }
+  set name(String v) { $_setString(2, 3, v); }
   bool hasName() => $_has(2, 3);
   void clearName() => clearField(3);
 }
@@ -460,17 +460,17 @@
   }
 
   M get m => $_get(0, 1, null);
-  void set m(M v) { setField(1, v); }
+  set m(M v) { setField(1, v); }
   bool hasM() => $_has(0, 1);
   void clearM() => clearField(1);
 
   p1.M get m1 => $_get(1, 2, null);
-  void set m1(p1.M v) { setField(2, v); }
+  set m1(p1.M v) { setField(2, v); }
   bool hasM1() => $_has(1, 2);
   void clearM1() => clearField(2);
 
   p2.M get m2 => $_get(2, 3, null);
-  void set m2(p2.M v) { setField(3, v); }
+  set m2(p2.M v) { setField(3, v); }
   bool hasM2() => $_has(2, 3);
   void clearM2() => clearField(3);
 }
diff --git a/test/message_generator_test.dart b/test/message_generator_test.dart
index e28c401..80bf551 100755
--- a/test/message_generator_test.dart
+++ b/test/message_generator_test.dart
@@ -65,17 +65,17 @@
   }
 
   String get number => $_get(0, 1, '');
-  void set number(String v) { $_setString(0, 1, v); }
+  set number(String v) { $_setString(0, 1, v); }
   bool hasNumber() => $_has(0, 1);
   void clearNumber() => clearField(1);
 
   PhoneNumber_PhoneType get type => $_get(1, 2, null);
-  void set type(PhoneNumber_PhoneType v) { setField(2, v); }
+  set type(PhoneNumber_PhoneType v) { setField(2, v); }
   bool hasType() => $_has(1, 2);
   void clearType() => clearField(2);
 
   String get name => $_get(2, 3, '\$');
-  void set name(String v) { $_setString(2, 3, v); }
+  set name(String v) { $_setString(2, 3, v); }
   bool hasName() => $_has(2, 3);
   void clearName() => clearField(3);
 }