Simplify nano flag to codegen to just 'nano' from 'nano=true'

'nano=true' still works, but any value is now ignored. This is to align
with our lite flag, but also just because It's Cleaner.

Note that this is counter to what javanano does. Javanano requires all
flags have a value and uses true/false for many values.
diff --git a/android-interop-testing/app/build.gradle b/android-interop-testing/app/build.gradle
index 3dfe35c..874cdf5 100644
--- a/android-interop-testing/app/build.gradle
+++ b/android-interop-testing/app/build.gradle
@@ -47,7 +47,7 @@
             task.plugins {
                 grpc {
                     // Options added to --grpc_out
-                    option 'nano=true'
+                    option 'nano'
                 }
             }
         }
diff --git a/compiler/README.md b/compiler/README.md
index e78c08d..d09a70b 100644
--- a/compiler/README.md
+++ b/compiler/README.md
@@ -40,7 +40,7 @@
 To generate Java interfaces with protobuf nano:
 ```
 $ protoc --plugin=protoc-gen-grpc-java=build/binaries/java_pluginExecutable/protoc-gen-grpc-java \
-  --grpc-java_out=nano=true:"$OUTPUT_FILE" --proto_path="$DIR_OF_PROTO_FILE" "$PROTO_FILE"
+  --grpc-java_out=nano:"$OUTPUT_FILE" --proto_path="$DIR_OF_PROTO_FILE" "$PROTO_FILE"
 ```
 
 ## Installing the codegen to Maven local repository
diff --git a/compiler/build.gradle b/compiler/build.gradle
index b9e4173..30c5dca 100644
--- a/compiler/build.gradle
+++ b/compiler/build.gradle
@@ -168,7 +168,7 @@
       }
       task.plugins {
         grpc {
-          option 'nano=true'
+          option 'nano'
         }
       }
     }
diff --git a/compiler/src/java_plugin/cpp/java_plugin.cpp b/compiler/src/java_plugin/cpp/java_plugin.cpp
index eb4a456..5b4b190 100644
--- a/compiler/src/java_plugin/cpp/java_plugin.cpp
+++ b/compiler/src/java_plugin/cpp/java_plugin.cpp
@@ -38,7 +38,7 @@
     java_grpc_generator::ProtoFlavor flavor =
         java_grpc_generator::ProtoFlavor::NORMAL;
     for (int i = 0; i < options.size(); i++) {
-      if (options[i].first == "nano" && options[i].second == "true") {
+      if (options[i].first == "nano") {
         flavor = java_grpc_generator::ProtoFlavor::NANO;
       } else if (options[i].first == "lite") {
         flavor = java_grpc_generator::ProtoFlavor::LITE;
diff --git a/examples/android/app/build.gradle b/examples/android/app/build.gradle
index 155b62f..462d658 100644
--- a/examples/android/app/build.gradle
+++ b/examples/android/app/build.gradle
@@ -46,7 +46,7 @@
             task.plugins {
                 grpc {
                     // Options added to --grpc_out
-                    option 'nano=true'
+                    option 'nano'
                 }
             }
         }