fix: use correct return type for cpp project. closes #343

Author: satya164

packages/create-react-native-library/templates/cpp-library/android/cpp-adapter.cpp

@@ -2,7 +2,7 @@
 #include "<%- project.identifier -%>.h"
 
 extern "C"
-JNIEXPORT jint JNICALL
+JNIEXPORT jdouble JNICALL
 Java_com_<%- project.package_cpp -%>_<%- project.name -%>Module_nativeMultiply(JNIEnv *env, jclass type, jdouble a, jdouble b) {
     return <%- project.package_cpp -%>::multiply(a, b);
 }

packages/create-react-native-library/templates/cpp-view-mixed/android/registration.cpp

@@ -15,4 +15,4 @@ void registerProviders() {
 JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *) {
     facebook::react::registerProviders();
     return JNI_VERSION_1_6;
-}
+}

packages/create-react-native-library/templates/cpp-view-new/android/registration.cpp

@@ -15,4 +15,4 @@ void registerProviders() {
 JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *) {
     facebook::react::registerProviders();
     return JNI_VERSION_1_6;
-}
+}