Increase leveldb version to 1.20.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=148937577

Makefile

@@ -122,7 +122,7 @@ SHARED_MEMENVLIB = $(SHARED_OUTDIR)/libmemenv.a
 else
 # Update db.h if you change these.
 SHARED_VERSION_MAJOR = 1
-SHARED_VERSION_MINOR = 19
+SHARED_VERSION_MINOR = 20
 SHARED_LIB1 = libleveldb.$(PLATFORM_SHARED_EXT)
 SHARED_LIB2 = $(SHARED_LIB1).$(SHARED_VERSION_MAJOR)
 SHARED_LIB3 = $(SHARED_LIB1).$(SHARED_VERSION_MAJOR).$(SHARED_VERSION_MINOR)

include/leveldb/db.h

@@ -14,7 +14,7 @@ namespace leveldb {
 
 // Update Makefile if you change these
 static const int kMajorVersion = 1;
-static const int kMinorVersion = 19;
+static const int kMinorVersion = 20;
 
 struct Options;
 struct ReadOptions;