Make v1beta the default api version (#123)

Also, update the README to use gemini-1.5-pro-latest

README.md

@@ -9,7 +9,7 @@ For example, with just a few lines of code, you can access Gemini's multimodal c
 
 ```kotlin
 val generativeModel = GenerativeModel(
-    modelName = "gemini-1.0-pro-vision-latest",
+    modelName = "gemini-1.5-pro-latest",
     apiKey = BuildConfig.apiKey
 )
 
@@ -30,15 +30,15 @@ print(response.text)
 
 This repository contains a sample app demonstrating how the SDK can access and utilize the Gemini model for various use cases.
 
-To try out the sample app you can directly import the project from Android Studio 
+To try out the sample app you can directly import the project from Android Studio
 via **File > New > Import Sample** and searching for *Generative AI Sample* or follow these steps below:
 
 1.  Check out this repository.\
 `git clone https://github.com/google/generative-ai-android`
 
 1.  [Obtain an API key](https://makersuite.google.com/app/apikey) to use with the Google AI SDKs.
 
-1.  Open and build the sample app in the `generativeai-android-sample` folder of this repo. 
+1.  Open and build the sample app in the `generativeai-android-sample` folder of this repo.
 
 1.  Paste your API key into the `apiKey` property in the `local.properties` file.
 

common/src/main/kotlin/com/google/ai/client/generativeai/common/RequestOptions.kt

@@ -30,13 +30,13 @@ import kotlin.time.toDuration
  */
 class RequestOptions(
   val timeout: Duration,
-  val apiVersion: String = "v1",
+  val apiVersion: String = "v1beta",
   val endpoint: String = "https://generativelanguage.googleapis.com",
 ) {
   @JvmOverloads
   constructor(
     timeout: Long? = HttpTimeout.INFINITE_TIMEOUT_MS,
-    apiVersion: String = "v1",
+    apiVersion: String = "v1beta",
     endpoint: String = "https://generativelanguage.googleapis.com",
   ) : this(
     (timeout ?: HttpTimeout.INFINITE_TIMEOUT_MS).toDuration(DurationUnit.MILLISECONDS),

generativeai/src/main/java/com/google/ai/client/generativeai/type/RequestOptions.kt

@@ -29,12 +29,12 @@ import kotlin.time.toDuration
  */
 class RequestOptions(
   val timeout: Duration,
-  val apiVersion: String = "v1",
+  val apiVersion: String = "v1beta",
 ) {
   @JvmOverloads
   constructor(
     timeout: Long? = Long.MAX_VALUE,
-    apiVersion: String = "v1",
+    apiVersion: String = "v1beta",
   ) : this(
     (timeout ?: Long.MAX_VALUE).toDuration(DurationUnit.MILLISECONDS),
     apiVersion,