add HTTPS pins for good, free CAs: cert.startcom.org & letsencrypt.org

These are two good options for easy, free HTTPS certificates.  This should
help, but not fix, #238 https://gitlab.com/fdroid/fdroidclient/issues/238

CHANGELOG.md

@@ -3,6 +3,11 @@
 * Fix crash when trying to install incompatible apps with the privileged
   installer
 
+* add support for free Certificate Authorities: https://cert.startcom.org and
+  https://letsencrypt.org
+
+* enable TLS v1.2 on all Android versions that support it
+
 ### 0.96 (2015-09-03)
 
 * Move the repo index update to a notification

F-Droid/src/org/fdroid/fdroid/FDroidCertPins.java

@@ -43,6 +43,18 @@ public class FDroidCertPins {
 
             // OU=EssentialSSL Wildcard, CN=*.panicbutton.io
             "cdae8cc70af09a55a7642d13f84241cba1c3a3e6",
+
+            // C=IL, O=StartCom Ltd., OU=Secure Digital Certificate Signing, CN=StartCom Certification Authority
+            // https://cert.startcom.org/
+            "234b71255613e130dde34269c9cc30d46f0841e0",
+
+            // C=US, O=Internet Security Research Group, CN=ISRG Root X1
+            // https://letsencrypt.org
+            "f816513cfd1b449f2e6b28a197221fb81f514e3c",
+
+            // C=US, O=IdenTrust, CN=IdenTrust Commercial Root CA 1
+            // cross-signer for https://letsencrypt.org
+            "87e3bf322427c1405d2736c381e01d1a71d4a039",
     };
 
     public static List<String> PINLIST = null;