[MINOR][R] Fix indents of sparkR welcome message to be consistent wit…

…h pyspark and spark-shell

## What changes were proposed in this pull request?

1. Removed empty space at the beginning of welcome message lines of sparkR to be consistent with welcome message of `pyspark` and `spark-shell`
2. Setting indent of logo message lines to 3 to be consistent with welcome message of `pyspark` and `spark-shell`

Output of `pyspark`:
```
Welcome to
      ____              __
     / __/__  ___ _____/ /__
    _\ \/ _ \/ _ `/ __/  '_/
   /__ / .__/\_,_/_/ /_/\_\   version 2.4.0
      /_/

Using Python version 3.6.6 (default, Jun 28 2018 11:07:29)
SparkSession available as 'spark'.
```

Output of `spark-shell`:
```
Spark session available as 'spark'.
Welcome to
      ____              __
     / __/__  ___ _____/ /__
    _\ \/ _ \/ _ `/ __/  '_/
   /___/ .__/\_,_/_/ /_/\_\   version 2.4.0
      /_/

Using Scala version 2.11.12 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_161)
Type in expressions to have them evaluated.
Type :help for more information.
```

## How was this patch tested?

Before:
Output of `sparkR`:
```
 Welcome to
    ____              __
   / __/__  ___ _____/ /__
  _\ \/ _ \/ _ `/ __/  '_/
 /___/ .__/\_,_/_/ /_/\_\   version  2.4.0
    /_/

 SparkSession available as 'spark'.
```
After:
```
Welcome to
      ____              __
     / __/__  ___ _____/ /__
    _\ \/ _ \/ _ `/ __/  '_/
   /___/ .__/\_,_/_/ /_/\_\   version 2.4.0
      /_/

SparkSession available as 'spark'.
```

Closes apache#23293 from AzureQ/master.

Authored-by: Qi Shao <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>

R/pkg/inst/profile/shell.R

@@ -33,19 +33,19 @@
   sc <- SparkR:::callJStatic("org.apache.spark.sql.api.r.SQLUtils", "getJavaSparkContext", spark)
   assign("sc", sc, envir = .GlobalEnv)
   sparkVer <- SparkR:::callJMethod(sc, "version")
-  cat("\n Welcome to")
+  cat("\nWelcome to")
   cat("\n")
-  cat("    ____              __", "\n")
-  cat("   / __/__  ___ _____/ /__", "\n")
-  cat("  _\\ \\/ _ \\/ _ `/ __/  '_/", "\n")
-  cat(" /___/ .__/\\_,_/_/ /_/\\_\\")
+  cat("      ____              __", "\n")
+  cat("     / __/__  ___ _____/ /__", "\n")
+  cat("    _\\ \\/ _ \\/ _ `/ __/  '_/", "\n")
+  cat("   /___/ .__/\\_,_/_/ /_/\\_\\")
   if (nchar(sparkVer) == 0) {
     cat("\n")
   } else {
-    cat("   version ", sparkVer, "\n")
+    cat("   version", sparkVer, "\n")
   }
-  cat("    /_/", "\n")
+  cat("      /_/", "\n")
   cat("\n")
 
-  cat("\n SparkSession available as 'spark'.\n")
+  cat("\nSparkSession available as 'spark'.\n")
 }