Update README.md and sample app to match versions with to be released library version (0.18.13)

Author: ViliusSutkus89

README.md

@@ -20,7 +20,7 @@ Sample application consumes under 30MB.
 [android-sample-app/app/build.gradle](android-sample-app/app/build.gradle) contains code to load the library as a dependency in Gradle.
 ```gradle
 dependencies {
-    implementation 'com.viliussutkus89:pdf2htmlex-android:0.18.12'
+    implementation 'com.viliussutkus89:pdf2htmlex-android:0.18.13'
 }
 ```
 

android-sample-app/app/build.gradle

@@ -8,8 +8,8 @@ android {
         applicationId "com.viliussutkus89.android.pdf2htmlex.sampleapp"
         minSdkVersion 19
         targetSdkVersion 29
-        versionCode 23
-        versionName '0.18.12'
+        versionCode 24
+        versionName '0.18.13'
     }
     splits {
         abi {
@@ -25,7 +25,7 @@ android {
 }
 
 dependencies {
-    implementation 'com.viliussutkus89:pdf2htmlex-android:0.18.12'
+    implementation 'com.viliussutkus89:pdf2htmlex-android:0.18.13'
 
     implementation 'com.google.android.gms:play-services-oss-licenses:17.0.0'